                            Halibut User Manual
                            ===================

Halibut is a free (MIT-licensed) documentation production system, able to
generate multiple output formats from the same input data. This document is
its user manual.

This manual is copyright 2004-2017 Simon Tatham. All rights reserved. You
may distribute this documentation under the MIT licence. See appendix A for
the licence text in full.

Chapter 1: Introduction to Halibut
----------------------------------

       Halibut is a multi-format documentation processing system.

       What that means is that you write your document once, in Halibut's
       input format, and then the Halibut program processes it into several
       output formats which all contain the same text. So, for example,
       if you want your application to have a Windows help file, and you
       also want the same documentation available in HTML on your web site,
       Halibut can do that for you.

   1.1 Output formats supported by Halibut

       Currently Halibut supports the following output formats:

        -  Plain ASCII text.

        -  HTML.

        -  Unix man page format.

        -  GNU Info format.

        -  PDF.

        -  PostScript.

        -  Windows HTML Help (.CHM).

        -  Old-style Windows Help (.HLP).

   1.2 Features supported by Halibut

       Here's a list of Halibut's notable features.

        -  Halibut automatically assigns sequential numbers to your
           chapters, sections and subsections, and keeps track of them for
           you. You supply a _keyword_ for each section, and then you can
           generate cross-references to that section using the keyword, and
           Halibut will substitute the correct section number. Also, in any
           output format where it makes sense, the cross-references will be
           hyperlinks to that section of the document.

        -  Halibut has some support for Unicode: you can include arbitrary
           Unicode characters in your document, and specify fallback text
           in case any output format doesn't support that character.

        -  Halibut's indexing support is comprehensive and carefully
           designed. It's easy to use in the simple case, but has powerful
           features that should make it possible to maintain a high-quality
           and useful index.

Chapter 2: Running Halibut
--------------------------

       In the simplest case, running Halibut is very easy. You provide a
       set of input files on its command line, and it produces a set of
       output files.

         $ halibut intro.but gettingstarted.but reference.but index.but

       This will generate a large set of output files:

        -  `output.txt' will be a plain text version of the input document.

        -  `output.chm' will be a Windows HTML Help version of the same
           thing. (Note that to do this Halibut does not require any
           external software such as a Help compiler. It _directly_
           generates Windows HTML Help files, and therefore it doesn't need
           to be run on Windows to do so: it can generate them even when
           run from an automated script on a Unix machine.)

        -  `output.hlp' and `output.cnt' will be an old-style Windows Help
           version of the same thing. (Most of the text is in `output.hlp';
           `output.cnt' contains additional contents data used by the
           Windows help topic selector. If you lose the latter, the former
           should still be usable, but it will look less modern.)

        -  `output.1' will be a Unix man page.

        -  The set of files `*.html' will contain an HTML version of the
           document. If you have configured Halibut to generate more than
           one HTML file (the default), then the file `Contents.html' will
           be the topmost one that users should be directed to initially.
           If you have configured Halibut to generate a single file, it
           will be called `Manual.html'.

        -  `output.info', and some additional files `output.info-1',
           `output.info-2' etc., will be files suitable for use with GNU
           `info'.

        -  `output.pdf' will be a printable PDF manual.

        -  `output.ps' will be a printable PostScript manual.

   2.1 Command-line options

       Halibut supports command-line options in case you don't want to use
       all of Halibut's output formats, or you want to configure the names
       of your output files, or you want to supply additional configuration
       on the command line. The supported options are listed here.

       Firstly, there are options which indicate which of the output
       formats you want Halibut to generate:

       --text[=_filename_]

           Specifies that you want to generate plain text output. You can
           optionally specify a file name (e.g. `--text=myfile.txt'), in
           which case Halibut will change the name of the output file as
           well.

       --html[=_filename_]

           Specifies that you want to generate HTML output. You can
           optionally specify a file name (e.g. `--html=myfile.html'), in
           which case Halibut will change the name of the output file as
           well. Specifying a file name here will also cause the HTML to
           be output in _only_ one file, instead of the usual behaviour of
           producing multiple files with links between them. If you want
           to produce multiple files and configure their names, you will
           need to use the more complete file name configuration directives
           given in section 4.2.1 (although you may want to do so on the
           command line, using the `-C' option).

       --xhtml[=_filename_]

           Synonym for `--html'.

       --chm[=_filename_]

           Specifies that you want to generate Windows HTML Help
           output. You can optionally specify a file name (e.g.
           `--chm=myfile.chm'), in which case Halibut will change the name
           of the output file as well.

       --winhelp[=_filename_]

           Specifies that you want to generate old-style Windows
           Help output. You can optionally specify a file name (e.g.
           `--winhelp=myfile.hlp'), in which case Halibut will change the
           name of the output file as well.

           Your output file name should end with `.hlp'; if it doesn't,
           Halibut will append it. Halibut will also generate a contents
           file (ending in `.cnt') alongside the file name you specify.

       --whlp[=_filename_]

           Synonym for `--winhelp'.

       --hlp[=_filename_]

           Synonym for `--winhelp'.

       --man[=_filename_]

           Specifies that you want to generate man page output. You can
           optionally specify a file name (e.g. `--man=myfile.5'), in which
           case Halibut will change the name of the output file as well.

       --info[=_filename_]

           Specifies that you want to generate GNU `info' output. You can
           optionally specify a file name (e.g. `--info=myfile.info'), in
           which case Halibut will change the name of the output file as
           well.

           Unless the `info' output format is configured not to (see
           section 4.6), Halibut will divide the `info' output into many
           small files. The extra files will have numeric suffixes on their
           names; so, for example, `output.info' might be accompanied by
           additional files `output.info-1', `output.info-2' and so on.

       --pdf[=_filename_]

           Specifies that you want to generate PDF output. You can
           optionally specify a file name (e.g. `--pdf=myfile.pdf'), in
           which case Halibut will change the name of the output file as
           well.

       --ps[=_filename_]

           Specifies that you want to generate PostScript output. You can
           optionally specify a file name (e.g. `--ps=myfile.ps'), in which
           case Halibut will change the name of the output file as well.

       If you do not specify any of the above options, Halibut will simply
       produce _all_ of its output formats.

       Also, there is an option which allows you to specify an arbitrary
       `\cfg' configuration directive (see section 3.6):

       -C_config-directive_:_value_[:_value_...]

           The text following `-C' is expected to be a colon-separated list
           of strings. (If you need a literal colon, you can escape it with
           a backslash: `\:'. If you need a literal _backslash_, you can do
           the same: `\\'.) These strings are used as the parts of a `\cfg'
           directive. So, for example, the option

             -Ctext-section-align:2:leftplus

           will translate into the configuration directive

             \cfg{text-section-align}{2}{leftplus}

           (Note that your shell may also take an interest in backslashes,
           particularly under Unix. You may find that the backslash with
           which you escape a colon must be doubled in order to make the
           shell pass it to Halibut at all, and to pass a doubled backslash
           to Halibut you might have to type four backslashes on your shell
           command line. This is not part of Halibut's own behaviour, and
           it cannot do anything about it.)

           Configuration directives created in this way take effect after
           all other input has been processed. (In most cases, this has the
           effect of overriding any other instances of the directive in the
           input.)

       The options which set the output file names actually work by
       implicitly generating these configuration directives. When you
       specify `--text=myfile.txt', for example, Halibut treats it
       identically to `--text -Ctext-filename:myfile.txt'. The Windows Help
       and man page formats work similarly. HTML is slightly different,
       since it also arranges for single-file output if you pass a
       filename to `--html'; so `--html=myfile.html' is equivalent to
       `--html -Chtml-single-filename:myfile.html -Chtml-leaf-level:0'.
       (See chapter 4 for explanations of all these configuration
       directives.)

       In addition to these, there are also a few other options:

       --input-charset=_charset_

           Changes the default assumed character set for all input files
           from ASCII to something else. (-Cinput-charset cannot be used
           for this, as -C directives are processed after all other input,
           so wouldn't affect any files.)

           Any \cfg{input-charset} directives within input files override
           this option.

           See section 3.6 for more information about the input character
           set.

       --list-charsets

           List character sets known to Halibut.

       --list-fonts

           List fonts known to Halibut, both those it intrinsically knows
           about and those found in its input files.

       --help

           Print a brief help message and exit immediately. (Don't confuse
           this with `--winhelp'!)

       --version

           Print information about Halibut's version number and exit
           immediately.

       --licence

           Display Halibut's licence (see also appendix A) and exit
           immediately.

       --license

           US English alternative spelling of `--licence'.

       --precise

           Report column numbers as well as line numbers when reporting
           errors in the Halibut input files.

Chapter 3: Halibut input format
-------------------------------

       This chapter describes the format in which you should write
       documents to be processed by Halibut.

   3.1 The basics

       Halibut's input files mostly look like ordinary ASCII text files;
       you can edit them with any text editor you like.

       Writing paragraphs of ordinary text is very simple: you just
       write ordinary text in the ordinary way. You can wrap a paragraph
       across more than one line using line breaks in the text file, and
       Halibut will ignore this when it rewraps the paragraph for each
       output format. To separate paragraphs, use a blank line (i.e. two
       consecutive line breaks). For example, a fragment of Halibut input
       looking like this:

         This is a line of text.
         This is another line of text.
         
         This line is separated from the previous one by a blank line.

       will produce two paragraphs looking like this:

         This is a line of text. This is another line of text.

         This line is separated from the previous one by a blank line.

       The first two lines of the input have been merged together into a
       single paragraph, and the line break in the input file was treated
       identically to the spaces between the individual words.

       Halibut is designed to have very few special characters. The
       only printable characters in Halibut input which will not be
       treated exactly literally in the output are the backslash (`\')
       and the braces (`{' and `}'). If you do not use these characters,
       _everything_ else you might type in normal ASCII text is perfectly
       safe. If you do need to use any of those three characters in your
       document, you will have to precede each one with a backslash. Hence,
       for example, you could write

         This \\ is a backslash, and these are \{braces\}.

       and Halibut would generate the text

         This \ is a backslash, and these are {braces}.

       If you want to write your input file in a character set other than
       ASCII, you can do so by using the `\cfg{input-charset}' command. See
       section 3.6 for details of this.

   3.2 Simple inline formatting commands

       Halibut formatting commands all begin with a backslash, followed
       by a word or character identifying the command. Some of them then
       use braces to surround one or more pieces of text acted on by the
       command. (In fact, the `\\', `\{' and `\}' sequences you met in
       section 3.1 are themselves formatting commands.)

       This section describes some simple formatting commands you can use
       in Halibut documents. The commands in this section are _inline_
       commands, which means you can use them in the middle of a paragraph.
       Section 3.3 describes some _paragraph_ commands, which affect a
       whole paragraph at a time.

       Many of these commands are followed by a pair of braces surrounding
       some text. In all cases, it is perfectly safe to have a line break
       (in the input file) within those braces; Halibut will treat that
       exactly the same as a space. For example, these two paragraphs will
       be treated identically:

         Here is some \e{emphasised
         text}.
         
         Here is some \e{emphasised text}.

 3.2.1 `\e' and `\s': Emphasising text

       Possibly the most obvious piece of formatting you might want to use
       in a document is _emphasis_. To emphasise text, you use the `\e'
       command, and follow it up with the text to be emphasised in braces.
       For example, the first sentence in this paragraph was generated
       using the Halibut input

         Possibly the most obvious piece of formatting you might want
         to use in a document is \e{emphasis}.

       A second form of emphasis is supported, called *strong* text. You
       can use the `\s' command for this type of emphasis. Typically, in
       output formats, `\e' will give italics, and `\s' will give bold.

 3.2.2 `\c' and `\cw': Displaying computer code inline

       Halibut was primarily designed to produce software manuals. It can
       be used for other types of document as well, but software manuals
       are its speciality.

       In software manuals, you often want to format text in a way that
       indicates that it is something you might see displayed verbatim on
       a computer screen. In printed manuals, this is typically done by
       setting that text in a font which is obviously fixed-width. This
       provides a visual cue that the text being displayed is code, and
       it also ensures that punctuation marks are clearly separated and
       shown individually (so that a user can copy the text accurately and
       conveniently).

       Halibut provides _two_ commands for this, which are subtly
       different. The names of those commands are `\c' (`code') and `\cw'
       (`weak code'). You use them just like `\e' and `\s', by following
       them with some text in braces. For example, this...

         This sentence contains some \c{code} and some \cw{weak code}.

       ... produces this:

         This sentence contains some `code' and some weak code.

       The distinction between code and weak code is mainly important when
       producing plain text output. Plain text output is typically viewed
       in a fixed-width font, so there is no need (and no way) to change
       font in order to make the order of punctuation marks clear. However,
       marking text as code is also _sometimes_ done to provide a visual
       distinction between it and the text around it, so that the reader
       knows where the literal computer text starts and stops; and in plain
       text, this cannot be done by changing font, so there needs to be an
       alternative way.

       So in the plain text output format, things marked as code (`\c')
       will be surrounded by quote marks, so that it's obvious where they
       start and finish. Things marked as weak code (`\cw') will not look
       any different from normal text.

       I recommend using weak code for any application where it is
       _obvious_ that the text is literal computer input or output. For
       example, if the text is capitalised, that's usually good enough. If
       I talk about the Pentium's EAX and EDX registers, for example, you
       don't need quotes to notice that those are special; so I would write
       that in Halibut as `the Pentium's \cw{EAX} and \cw{EDX} registers'.
       But if I'm talking about the Unix command `man', which is an
       ordinary English word in its own right, a reader might be slightly
       confused if it appeared in the middle of a sentence undecorated; so
       I would write that as `the Unix command \c{man}'.

       In summary:

        -  `\c' means `this text _must_ be visually distinct from the text
           around it'. Halibut's various output formats will do this by
           changing the font if possible, or by using quotes if not.

        -  `\cw' means `it would be nice to display this text in a fixed-
           width font if possible, but it's not essential'.

       In really extreme cases, you might want Halibut to use quotation
       marks even in output formats which can change font. In section
       3.2.5, for example, I mention the special formatting command `\.'.
       If that appeared at the end of a sentence _without_ the quotes, then
       the two adjacent full stops would look pretty strange even if they
       were obviously in different fonts.

       For this, Halibut supports the `\cq' command, which is exactly
       equivalent to using `\q' to provide quotes and then using `\cw'
       inside the quotes. So in the paragraph above, for example, I wrote

         the special formatting command \cq{\\.}.

       and I could equivalently have written

         the special formatting command \q{\cw{\\.}}.

       There is a separate mechanism for displaying computer code in an
       entire paragraph; see section 3.3.1 for that one.

 3.2.3 `\q': Quotation marks

       Halibut's various output formats don't all use the same conventions
       for displaying text in ordinary quotation marks (`like these').
       Some output formats have access to proper matched quote characters,
       whereas others are restricted to using plain ASCII. Therefore, it is
       not ideal to use the ordinary ASCII double quote character in your
       document (although you can if you like).

       Halibut provides the formatting command `\q' to indicate quoted
       text. If you write

         Here is some \q{text in quotes}.

       then Halibut will print

         Here is some `text in quotes'.

       and in every output format Halibut generates, it will choose the
       best quote characters available to it in that format. (The quote
       characters to use can be configured with the `\cfg' command.)

       You can still use the ordinary quote characters of your choice if
       you prefer; or you could even use the `\u' command (see section
       3.2.7) to generate Unicode matched quotes (single or double) in
       a way which will automatically fall back to the normal ASCII one
       if they aren't available. But I recommend using the built-in `\q'
       command in most cases, because it's simple and does the best it can
       everywhere.

       If you're using the `\c' or `\cw' commands to display literal
       computer code, you will probably want to use literal ASCII quote
       characters, because it is likely to matter precisely which quote
       character you use. In fact, Halibut actually _disallows_ the use of
       `\q' within either of `\c' and `\cw', since this simplifies some of
       the output formats.

 3.2.4 `\-' and `\_': Non-breaking hyphens and spaces

       If you use an ordinary hyphen in the middle of a word (such as
       `built-in'), Halibut's output formats will feel free to break a
       line after that hyphen when wrapping paragraphs. This is fine for
       a word like `built-in', but if you were displaying some literal
       computer code such as the Emacs command `M-x psychoanalyze-pinhead',
       you might prefer to see the whole hyphenated word treated as an
       unbreakable block. In some cases, you might even want to prevent the
       _space_ in that command from becoming a line break.

       For these purposes, Halibut provides the commands `\-' and `\_',
       which generate a non-breaking hyphen and a non-breaking space
       respectively. So the above Emacs command might be written as

         the Emacs command \c{M\-x\_psychoanalyze\-pinhead}

       Unfortunately, some of Halibut's output formats do not support non-
       breaking hyphens, and others don't support _breaking_ hyphens! So
       Halibut cannot promise to honour these commands in all situations.
       All it can do is make a best effort.

 3.2.5 `\date': Automatic date generation

       Sometimes you might want your document to give an up-to-date
       indication of the date on which it was run through Halibut.

       Halibut supplies the `\date' command to do this. In its simplest
       form, you simply say

         This document was generated on \date.

       and Halibut generates something like

         This document was generated on Fri Dec 24 23:51:50 2021.

       You can follow the `\date' command directly with punctuation (as
       in this example, where it is immediately followed by a full stop),
       but if you try to follow it with an alphabetic or numeric character
       (such as writing `\dateZ') then Halibut will assume you are trying
       to invoke the name of a macro command you have defined yourself, and
       will complain if no such command exists. To get round this you can
       use the special `\.' do-nothing command. See section 3.7 for more
       about general Halibut command syntax and `\.'.

       If you would prefer the date to be generated in a specific format,
       you can follow the `\date' command with a format specification in
       braces. The format specification will be run through the standard C
       function `strftime', so any format acceptable to that function is
       acceptable here as well. I won't document the format here, because
       the details vary from computer to computer (although there is a
       standard core which should be supported everywhere). You should look
       at your local system's manual for `strftime' for details.

       Here's an example which generates the date in the international
       standard ISO 8601 format:

         This document was generated on \date{%Y-%m-%d %H:%M:%S}.

       And here's some sample output from that command:

         This document was generated on 2021-12-24 23:51:50.

 3.2.6 `\W': WWW hyperlinks

       Since one of Halibut's output formats is HTML, it's obviously useful
       to be able to provide links to arbitrary web sites in a Halibut
       document.

       This is done using the `\W' command. `\W' expects to be followed by
       _two_ sets of braces. In the first set of braces you put a URL; in
       the second set you put the text which should be a hyperlink. For
       example, you might write

         Try searching on \W{http://www.google.com/}{Google}.

       and Halibut would generate

         Try searching on Google.

       Note that hyperlinks, like the non-breaking commands discussed in
       section 3.2.4, are _discretionary_: if an output format does not
       support them then they will just be left out completely. So unless
       you're _only_ intending to use the HTML output format, you should
       avoid storing vital content in the URL part of a `\W' command. The
       Google example above is reasonable (because most users are likely
       to be able to find Google for themselves even without a convenient
       hyperlink leading straight there), but if you really need to direct
       users to a specific web site, you will need to give the URL in
       actual displayed text (probably displayed as code as well). However,
       there's nothing to stop you making it a hyperlink _as well_ for the
       convenience of HTML readers.

       The `\W' command supports a piece of extra syntax to make this
       convenient for you. You can specify `\c' or `\cw' _between_ the
       first and second pairs of braces. For example, you might write

         Google is at \W{http://www.google.com/}\cw{www.google.com}.

       and Halibut would produce

         Google is at www.google.com.

       If you want the link text to be an index term as well, you can also
       specify `\i' or `\ii'; this has to come before `\c' or `\cw' if both
       are present. (See section 3.5 for more about indexing.)

 3.2.7 `\u': Specifying arbitrary Unicode characters

       Halibut has extensive support for Unicode and character set
       conversion. You can specify any (reasonably well known) character
       set for your input document, and Halibut will convert it all to
       Unicode as it reads it in. See section 3.6 for more details of this.

       If you need to specify a Unicode character in your input document
       which is not supported by the input character set you have chosen,
       you can use the `\u' command to do this. `\u' expects to be followed
       by a sequence of hex digits; so that `\u0041', for example, denotes
       the Unicode character 0x0041, which is the capital letter A.

       If a Unicode character specified in this way is not supported in
       a particular _output_ format, you probably don't just want it to
       be omitted. So you can put a pair of braces after the `\u' command
       containing fallback text. For example, to specify an amount of money
       in euros, you might write this:

         This is likely to cost \u20AC{EUR\_}2500 at least.

       Halibut will render that as a Euro sign _if available_, and the text
       `EUR ' if not. In the output format you're currently reading in, the
       above input generates this:

         This is likely to cost EUR 2500 at least.

       If you read it in other formats, you may see different results.

 3.2.8 `\k' and `\K': Cross-references to other sections

       Section 1.2 mentions that Halibut numbers the sections of your
       document automatically, and can generate cross-references to them
       on request. `\k' and `\K' are the commands used to generate those
       cross-references.

       To use one of these commands, you simply follow it with a pair of
       braces containing the keyword for the section in question. For
       example, you might write something like

         \K{input-xref} expands on \k{intro-features}.

       and Halibut would generate something like

         Section 3.2.8 expands on section 1.2.

       The keywords `input-xref' and `intro-features' are section keywords
       used in this manual itself. In your own document, you would have
       supplied a keyword for each one of your own sections, and you would
       provide your own keywords for the `\k' command to work on.

       The difference between `\k' and `\K' is simply that `\K' starts the
       cross-reference text with a capital letter; so you would use `\K' at
       the beginning of a sentence, and `\k' everywhere else.

       In output formats which permit it, cross-references act as
       hyperlinks, so that clicking the mouse on a cross-reference takes
       you straight to the referenced section.

       The `\k' commands are also used for referring to entries in a
       bibliography (see section 3.4 for more about bibliographies), and
       can also be used for referring to an element of a numbered list by
       its number (see section 3.3.2.2 for more about numbered lists).

       See section 3.3.5 for more about chapters and sections.

 3.2.9 `\#': Inline comments

       If you want to include comments in your Halibut input, to be seen
       when reading it directly but not copied into the output text, then
       you can use `\#' to do this. If you follow `\#' with text in braces,
       that text will be ignored by Halibut.

       For example, you might write

         The typical behaviour of an antelope \#{do I mean
         gazelle?} is...

       and Halibut will simply leave out the aside about gazelles, and will
       generate nothing but

         The typical behaviour of an antelope is...

       This command will respect nested braces, so you can use it to
       comment out sections of Halibut markup:

         This function is \#{very, \e{very}} important.

       In this example, the comment lasts until the final closing brace (so
       that the whole `very, _very_' section is commented out).

       The `\#' command can also be used to produce a whole-paragraph
       comment; see section 3.3.7 for details of that.

   3.3 Paragraph-level commands

       This section describes Halibut commands which affect an entire
       paragraph, or sometimes even _more_ than one paragraph, at a time.

 3.3.1 `\c': Displaying whole paragraphs of computer code

       Section 3.2.2 describes a mechanism for displaying computer code in
       the middle of a paragraph, a few words at a time.

       However, this is often not enough. Often, in a computer manual, you
       really want to show several lines of code in a display paragraph.

       This is also done using the `\c' command, in a slightly different
       way. Instead of using it in the middle of a paragraph followed by
       braces, you can use it at the start of each line of a paragraph. For
       example, you could write

         \c #include <stdio.h>
         \c
         \c int main(int argc, char **argv) {
         \c     printf("hello, world\n");
         \c     return 0;
         \c }

       and Halibut would generate

           #include <stdio.h>
           
           int main(int argc, char **argv) {
               printf("hello, world\n");
               return 0;
           }

       Note that the above paragraph makes use of a backslash and a pair
       of braces, and does _not_ need to escape them in the way described
       in section 3.1. This is because code paragraphs formatted in this
       way are a special case; the intention is that you can just copy and
       paste a lump of code out of your program, put `\c ' at the start of
       every line, and simply _not have to worry_ about the details - you
       don't have to go through the whole block looking for characters to
       escape.

       Since a backslash inside a code paragraph generates a literal
       backslash, this means you cannot use any other Halibut formatting
       commands inside a code paragraph. In particular, if you want to
       emphasise or strengthen a particular word in the paragraph, you
       can't do that using `\e' or `\s' (section 3.2.1) in the normal way.

       Therefore, Halibut provides an alternative means of emphasis in code
       paragraphs. Each line beginning with `\c' can optionally be followed
       by a single line beginning with `\e', indicating the emphasis in
       that line. The emphasis line contains the letters `b' and `i' (for
       `bold' and `italic', although some output formats might render `i'
       as underlining instead of italics), positioned to line up under the
       parts of the text that you want emphasised.

       For example, if you wanted to do syntax highlighting on the above
       C code by highlighting the preprocessor command in italic and the
       keywords in bold, you might do it like this:

         \c #include <stdio.h>
         \e iiiiiiiiiiiiiiiiii
         \c
         \c int main(int argc, char **argv) {
         \e bbb      bbb       bbbb
         \c     printf("hello, world\n");
         \c     return 0;
         \e     bbbbbb
         \c }

       and Halibut would generate:

           #include <stdio.h>
           
           int main(int argc, char **argv) {
               printf("hello, world\n");
               return 0;
           }

       Note that not every `\c' line has to be followed by a `\e' line;
       they're optional.

       Also, note that highlighting within a code paragraph is
       _discretionary_. Not all of Halibut's output formats can support it
       (plain text, in particular, has no sensible way to do it). Unless
       you know you are using a restricted range of output formats, you
       should use highlighting in code paragraphs _only_ as a visual aid,
       and not rely on it to convey any vital semantic content.

 3.3.2 `\b', `\n', `\dt', `\dd', `\lcont': Lists

       Halibut supports bulletted lists, numbered lists and description
       lists.

3.3.2.1 `\b': Bulletted lists

       To create a bulletted list, you simply prefix each paragraph
       describing a bullet point with the command `\b'. For example, this
       Halibut input:

         Here's a list:
         
         \b One.
         
         \b Two.
         
         \b Three.

       would produce this Halibut output:

         Here's a list:

          -  One.

          -  Two.

          -  Three.

3.3.2.2 `\n': Numbered lists

       Numbered lists are just as simple: instead of `\b', you use `\n',
       and Halibut takes care of getting the numbering right for you. For
       example:

         Here's a list:
         
         \n One.
         
         \n Two.
         
         \n Three.

       This produces the Halibut output:

         Here's a list:

          1. One.

          2. Two.

          3. Three.

       The disadvantage of having Halibut sort out the list numbering for
       you is that if you need to refer to a list item by its number, you
       can't reliably know the number in advance (because if you later add
       another item at the start of the list, the numbers will all change).
       To get round this, Halibut allows an optional keyword in braces
       after the `\n' command. This keyword can then be referenced using
       the `\k' or `\K' command (see section 3.2.8) to provide the number
       of the list item. For example:

         Here's a list:
         
         \n One.
         
         \n{this-one} Two.
         
         \n Three.
         
         \n Now go back to step \k{this-one}.

       This produces the following output:

         Here's a list:

          1. One.

          2. Two.

          3. Three.

          4. Now go back to step 2.

       The keyword you supply after `\n' is allowed to contain escaped
       special characters (`\\', `\{' and `\}'), but should not contain any
       other Halibut markup. It is intended to be a word or two of ordinary
       text. (This also applies to keywords used in other commands, such as
       `\B' and `\C').

3.3.2.3 `\dt' and `\dd': Description lists

       To write a description list, you prefix alternate paragraphs with
       the `\dt' (`described thing') and `\dd' (description) commands. For
       example:

         \dt Pelican
         
         \dd This is a large bird with a big beak.
         
         \dt Panda
         
         \dd This isn't.

       This produces the following output:

         Pelican

             This is a large bird with a big beak.

         Panda

             This isn't.

       If you really want to, you are allowed to use `\dt' and `\dd'
       without strictly interleaving them (multiple consecutive `\dt's or
       consecutive `\dd's, or a description list starting with `\dd' or
       ending with `\dt'). This is probably most useful if you are listing
       a sequence of things with `\dt', but only some of them actually need
       `\dd' descriptions. You should _not_ use multiple consecutive `\dd's
       to provide a multi-paragraph definition of something; that's what
       `\lcont' is for, as explained in section 3.3.2.4.

3.3.2.4 Continuing list items into further paragraphs

       All three of the above list types assume that each list item is a
       single paragraph. For a short, snappy list in which each item is
       likely to be only one or two words, this is perfectly sufficient;
       but occasionally you will find you want to include several
       paragraphs in a single list item, or even to nest other types of
       paragraph (such as code paragraphs, or other lists) inside a list
       item.

       To do this, you use the `\lcont' command. This is a command which
       can span _multiple_ paragraphs.

       After the first paragraph of a list item, include the text
       `\lcont{'. This indicates that the subsequent paragraph(s) are a
       _continuation_ of the list item that has just been seen. So you
       can include further paragraphs, and eventually include a closing
       brace `}' to finish the list continuation. After that, you can
       either continue adding other items to the original list, or stop
       immediately and return to writing normal paragraphs of text.

       Here's a (long) example.

         Here's a list:
         
         \n One. This item is followed by a code paragraph:
         
         \lcont{
         
         \c code
         \c paragraph
         
         }
         
         \n Two. Now when I say \q{two}, I mean:
         
         \lcont{
         
         \n Two, part one.
         
         \n Two, part two.
         
         \n Two, part three.
         
         }
         
         \n Three.

       The output produced by this fragment is:

         Here's a list:

          1. One. This item is followed by a code paragraph:

               code
               paragraph

          2. Two. Now when I say `two', I mean:

              1. Two, part one.

              2. Two, part two.

              3. Two, part three.

          3. Three.

       This syntax might seem a little bit inconvenient, and perhaps
       counter-intuitive: you might expect the enclosing braces to have to
       go around the _whole_ list item, rather than everything except the
       first paragraph.

       `\lcont' is a recent addition to the Halibut input language;
       previously, _all_ lists were required to use no more than one
       paragraph per list item. So it's certainly true that this feature
       looks like an afterthought because it _is_ an afterthought, and it's
       possible that if I'd been designing the language from scratch with
       multiple-paragraph list items in mind, I would have made it look
       different.

       However, the advantage of doing it this way is that no enclosing
       braces are required in the _common_ case: simple lists with only one
       paragraph per item are really, really easy to write. So I'm not too
       unhappy with the way it turned out; it obeys the doctrine of making
       simple things simple, and difficult things possible.

       Note that `\lcont' can only be used on `\b', `\n' and `\dd'
       paragraphs; it cannot be used on `\dt'.

 3.3.3 `\rule': Horizontal rules

       The command `\rule', appearing on its own as a paragraph, will cause
       a horizontal rule to be drawn, like this:

         Some text.
         
         \rule
         
         Some more text.

       This produces the following output:

         Some text.

         ------------------------------------------------------------------

         Some more text.

 3.3.4 `\quote': Indenting multiple paragraphs as a long quotation

       Quoting verbatim text using a code paragraph (section 3.3.1) is not
       always sufficient for your quoting needs. Sometimes you need to
       quote some normally formatted text, possibly in multiple paragraphs.
       This is similar to HTML's <BLOCKQUOTE> command.

       To do this, you can use the `\quote' command. Like `\lcont', this
       is a command which expects to enclose at least one paragraph and
       possibly more. Simply write `\quote{' at the beginning of your
       quoted section, and `}' at the end, and the paragraphs in between
       will be formatted to indicate that they are a quotation.

       (This very manual, in fact, uses this feature a lot: all of the
       examples of Halibut input followed by Halibut output have the output
       quoted using `\quote'.)

       Here's some example Halibut input:

         In \q{Through the Looking Glass}, Lewis Carroll wrote:
         
         \quote{
         
         \q{The question is,} said Alice, \q{whether you \e{can} make
         words mean so many different things.}
         
         \q{The question is,} said Humpty Dumpty, \q{who is to be
         master - that's all.}
         
         }
         
         So now you know.

       The output generated by this is:

         In `Through the Looking Glass', Lewis Carroll wrote:

           `The question is,' said Alice, `whether you _can_ make words
           mean so many different things.'

           `The question is,' said Humpty Dumpty, `who is to be master -
           that's all.'

         So now you know.

 3.3.5 `\C', `\H', `\S', `\A', `\U': Chapter and section headings

       Section 1.2 mentions that Halibut numbers the sections of your
       document automatically, and can generate cross-references to them on
       request; section 3.2.8 describes the `\k' and `\K' commands used to
       generate the cross-references. This section describes the commands
       used to set up the sections in the first place.

       A paragraph beginning with the `\C' command defines a chapter
       heading. The `\C' command expects to be followed by a pair of braces
       containing a keyword for the chapter; this keyword can then be used
       with the `\k' and `\K' commands to generate cross-references to
       the chapter. After the closing brace, the rest of the paragraph is
       used as the displayed chapter title. So the heading for the current
       chapter of this manual, for example, is written as

         \C{input} Halibut input format

       and this allows me to use the command `\k{input}' to generate a
       cross-reference to that chapter somewhere else.

       The keyword you supply after one of these commands is allowed to
       contain escaped special characters (`\\', `\{' and `\}'), but should
       not contain any other Halibut markup. It is intended to be a word or
       two of ordinary text. (This also applies to keywords used in other
       commands, such as `\B' and `\n').

       The next level down from `\C' is `\H', for `heading'. This is used
       in exactly the same way as `\C', but section headings defined with
       `\H' are considered to be part of a containing chapter, and will
       be numbered with a pair of numbers. After `\H' comes `\S', and if
       necessary you can then move on to `\S2', `\S3' and so on.

       For example, here's a sequence of heading commands. Normally these
       commands would be separated at least by blank lines (because each is
       a separate paragraph), and probably also by body text; but for the
       sake of brevity, both of those have been left out in this example.

         \C{foo} Using Foo
         \H{foo-intro} Introduction to Foo
         \H{foo-running} Running the Foo program
         \S{foo-inter} Running Foo interactively
         \S{foo-batch} Running Foo in batch mode
         \H{foo-trouble} Troubleshooting Foo
         \C{bar} Using Bar instead of Foo

       This would define two chapters with keywords `foo' and `bar', which
       would end up being called Chapter 1 and Chapter 2 (unless there were
       other chapters before them). The sections `foo-intro', `foo-running'
       and `foo-trouble' would be referred to as Section 1.1, Section 1.2
       and Section 1.3 respectively; the subsections `foo-inter' and `foo-
       batch' would be Section 1.2.1 and Section 1.2.2. If there had been a
       `\S2' command within one of those, it would have been something like
       Section 1.2.1.1.

       If you don't like the switch from `\H' to `\S', you can use `\S1'
       as a synonym for `\S' and `\S0' as a synonym for `\H'. Chapters are
       still designated with `\C', because they need to be distinguished
       from other types of chapter such as appendices. (Personally, I like
       the `\C',`\H',`\S' notation because it encourages me to think of my
       document as a hard disk :-)

       You can define an appendix by using `\A' in place of `\C'. This is
       no different from a chapter except that it's given a letter instead
       of a number, and cross-references to it will say `Appendix A'
       instead of `Chapter 9'. Subsections of an appendix will be numbered
       `A.1', `A.2', `A.2.1' and so on.

       If you want a particular section to be referred to as something
       other than a `chapter', `section' or `appendix', you can include
       a second pair of braces after the keyword. For example, if you're
       writing a FAQ chapter and you want cross-references between
       questions to refer to `question 1.2.3' instead of `section 1.2.3',
       you can write each section heading as

         \S{question-about-fish}{Question} What about fish?

       (The word `Question' should be given with an initial capital letter.
       Halibut will lower-case it when you refer to it using `\k', and will
       leave it alone if you use `\K'.)

       This technique allows you to change the designation of _particular_
       sections. To make an overall change in what _every_ section is
       called, see section 3.6.

       Finally, the `\U' command defines an _unnumbered_ chapter.
       These sometimes occur in books, for specialist purposes such as
       `Bibliography' or `Acknowledgements'. `\U' does not expect a keyword
       argument, because there is no sensible way to generate an automatic
       cross-reference to such a chapter anyway.

 3.3.6 `\copyright', `\title', `\versionid': Miscellaneous blurb commands

       These three commands define a variety of special paragraph types.
       They are all used in the same way: you put the command at the start
       of a paragraph, and then just follow it with normal text, like this:

         \title My First Manual

       The three special paragraph types are:

       \title

           This defines the overall title of the entire document. This
           title is treated specially in some output formats (for example,
           it's used in a <TITLE> tag in the HTML output), so it needs a
           special paragraph type to point it out.

       \copyright

           This command indicates that the paragraph attached to it
           contains a copyright statement for the document. This text
           is displayed inline where it appears, exactly like a normal
           paragraph; but in some output formats it is given additional
           special treatment. For example, Windows Help files have a
           standard slot in which to store a copyright notice, so that
           other software can display it prominently.

       \versionid

           This command indicates that the paragraph contains a version
           identifier, such as those produced by CVS (of the form
           `$Id: thingy.but,v 1.6 2004/01/01 16:47:48 simon Exp $'). This
           text will be tucked away somewhere unobtrusive, so that anyone
           wanting to (for example) report errors to the document's author
           can pick out the version IDs and send them as part of the
           report, so that the author can tell at a glance which revision
           of the document is being discussed.

 3.3.7 `\#': Whole-paragraph comments

       Section 3.2.9 describes the use of the `\#' command to put a short
       comment in the middle of a paragraph.

       If you need to use a _long_ comment, Halibut also allows you to
       use `\#' without braces, to indicate that an entire paragraph is a
       comment, like this:

         Here's a (fairly short) paragraph which will be displayed.
         
         \# Here's a comment paragraph which will not be displayed, no
         matter how long it goes on. All I needed to indicate this was
         the single \# at the start of the paragraph; I don't need one
         on every line or anything like that.
         
         Here's another displayed paragraph.

       When run through Halibut, this produces the following output:

         Here's a (fairly short) paragraph which will be displayed.

         Here's another displayed paragraph.

   3.4 Creating a bibliography

       If you need your document to refer to other documents (research
       papers, books, websites, whatever), you might find a bibliography
       feature useful.

       You can define a bibliography entry using the `\B' command. This
       looks very like the `\C' command and friends: it expects a keyword
       in braces, followed by some text describing the document being
       referred to. For example:

         \B{freds-book} \q{The Taming Of The Mongoose}, by Fred Bloggs.
         Published by Paperjam & Notoner, 1993.

       If this bibliography entry appears in the finished document, it will
       look something like this:

         [1] `The Taming Of The Mongoose', by Fred Bloggs. Published by
         Paperjam & Notoner, 1993.

       I say `if' above because not all bibliography entries defined using
       the `\B' command will necessarily appear in the finished document.
       They only appear if they are referred to by a `\k' command (see
       section 3.2.8). This allows you to (for example) maintain a single
       Halibut source file with a centralised database of _all_ the
       references you have ever needed in any of your writings, include
       that file in every document you feed to Halibut, and have it
       only produce the bibliography entries you actually need for each
       particular document. (In fact, you might even want this centralised
       source file to be created automatically by, say, a Perl script from
       BibTeX input, so that you can share the same bibliography with users
       of other formatting software.)

       If you really want a bibliography entry to appear in the document
       even though no text explicitly refers to it, you can do that using
       the `\nocite' command:

         \nocite{freds-book}

       Normally, each bibliography entry will be referred to (in citations
       and in the bibliography itself) by a simple reference number, such
       as [1]. If you would rather use an alternative reference notation,
       such as [Fred1993], you can use the `\BR' (`Bibliography Rewrite')
       command to specify your own reference format for a particular book:

         \BR{freds-book} [Fred1993]

       The keyword you supply after `\B' is allowed to contain escaped
       special characters (`\\', `\{' and `\}'), but should not contain any
       other Halibut markup. It is intended to be a word or two of ordinary
       text. (This also applies to keywords used in other commands, such as
       `\n' and `\C').

   3.5 Creating an index

       Halibut contains a comprehensive indexing mechanism, which attempts
       to be reasonably easy to use in the common case in spite of its
       power.

 3.5.1 Simple indexing

       In normal usage, you should be able to add index terms to your
       document simply by using the `\i' command to wrap one or two words
       at a time. For example, if you write

         The \i{hippopotamus} is a particularly large animal.

       then the index will contain an entry under `hippopotamus', pointing
       to that sentence (or as close to that sentence as the output format
       sensibly permits).

       You can wrap more than one word in `\i' as well:

         We recommend using a \i{torque wrench} for this job.

 3.5.2 Special cases of indexing

       If you need to index a computer-related term, you can use the
       special case `\i\c' (or `\i\cw' if you prefer):

         The \i\c{grep} command is what you want here.

       This will cause the word `grep' to appear in code style, as if the
       `\i' were not present and the input just said `\c{grep}'; the word
       will also appear in code style in the actual index.

       If you want to simultaneously index and emphasise a word, there's
       another special case `\i\e' (and similarly `\i\s'):

         This is what we call a \i\e{paper jam}.

       This will cause the words `paper jam' to be emphasised in the
       document, but (unlike the behaviour of `\i\c') they will _not_ be
       emphasised in the index. This different behaviour is based on an
       expectation that most people indexing a word of computer code will
       still want it to look like code in the index, whereas most people
       indexing an emphasised word will _not_ want it emphasised in the
       index.

       (In fact, _no_ emphasis in the text inside `\i' will be preserved
       in the index. If you really want a term in the index to appear
       emphasised, you must say so explicitly using `\IM'; see section
       3.5.3.)

       Sometimes you might want to index a term which is not explicitly
       mentioned, but which is highly relevant to the text and you think
       that somebody looking up that term in the index might find it useful
       to be directed here. To do this you can use the `\I' command, to
       create an _invisible_ index tag:

         If your printer runs out of toner, \I{replacing toner
         cartridge}here is what to do:

       This input will produce only the output `If your printer runs out of
       toner, here is what to do'; but an index entry will show up under
       `replacing toner cartridge', so that if a user thinks the obvious
       place to start in the index is under R for `replacing', they will
       find their way here with a minimum of fuss.

       (It's worth noting that there is no functional difference between
       `\i{foo}' and `\I{foo}foo'. The simple `\i' case is only a shorthand
       for the latter.)

       Finally, if you want to index a word at the start of a sentence,
       you might very well not want it to show up with a capital letter in
       the index. For this, Halibut provides the `\ii' command, for `index
       (case-)insensitively'. You use it like this:

         \ii{Lions} are at the top of the food chain in this area.

       This is equivalent to `\I{lions}Lions'; in other words, the text
       will say `Lions', but it will show up in the index as `lions'. The
       text inside `\ii' is converted entirely into lower case before being
       added to the index data.

 3.5.3 Fine-tuning the index

       Halibut's index mechanism as described so far still has a few
       problems left:

        -  In a reasonably large index, it's often difficult to predict
           which of several words a user will think of first when trying
           to look something up. For example, if they want to know how to
           replace a toner cartridge, they might look up `replacing' or
           they might look up `toner cartridge'. You probably don't really
           want to have to try to figure out which of those is more likely;
           instead, what you'd like is to be able to effortlessly index the
           same set of document locations under _both_ terms.

        -  Also, you may find you've indexed the same concept under
           multiple different index terms; for example, there might be
           several instances of `\i{frog}' and several of `\i{frogs}',
           so that you'd end up with two separate index entries for what
           really ought to be the same concept.

        -  You might well not want the word `grep' to appear in the index
           without explanation; you might prefer it to say something more
           verbose such as `grep command', so that a user encountering
           it in the index has some idea of what it is _without_ having
           to follow up the reference. However, you certainly don't want
           to have to write `\I{\cw{grep} command}\c{grep}' every time
           you want to add an index term for this! You wanted to write
           `\i\c{grep}' as shown in the previous section, and tidy it all
           up afterwards.

       All of these problems can be cleaned up by the `\IM' (for `Index
       Modification') command. `\IM' expects to be followed by one or more
       pairs of braces containing index terms as seen in the document, and
       then a piece of text (not in braces) describing how it should be
       shown in the index.

       So to rewrite the `grep' example above, you might do this:

         \IM{grep} \cw{grep} command

       This will arrange that the set of places in the document where you
       asked Halibut to index `grep' will be listed under `grep command'
       rather than just under `grep'.

       You can specify more than one index term in a `\IM' command; so to
       merge the index terms `frog' and `frogs' into a single term, you
       might do this:

         \IM{frog}{frogs} frog

       This will arrange that the single index entry `frog' will list _all_
       the places in the document where you asked Halibut to index either
       `frog' or `frogs'.

       You can use multiple `\IM' commands to replicate the same set of
       document locations in more than one index entry. For example:

         \IM{replacing toner cartridge} replacing toner cartridge
         \IM{replacing toner cartridge} toner cartridge, replacing

       This will arrange that every place in the document where you have
       indexed `replacing toner cartridge' will be listed both there _and_
       under `toner cartridge, replacing', so that no matter whether the
       user looks under R or under T they will stil find their way to the
       same parts of the document.

       In this example, note that although the first `\IM' command _looks_
       as if it's a tautology, it is still necessary, because otherwise
       those document locations will _only_ be indexed under `toner
       cartridge, replacing'. If you have _no_ explicit `\IM' commands for
       a particular index term, then Halibut will assume a default one
       (typically `\IM{foo} foo', although it might be `\IM{foo} \c{foo}'
       if you originally indexed using `\i\c'); but as soon as you specify
       an explicit `\IM', Halibut discards its default implicit one, and
       you must then specify that one explicitly as well if you wanted to
       keep it.

 3.5.4 Indexing terms that differ only in case

       The _tags_ you use to define an index term (that is, the text in the
       braces after `\i', `\I' and `\IM') are treated case-insensitively by
       Halibut. So if, as in this manual itself, you need two index terms
       that differ only in case, doing this will not work:

         The \i\c{\\c} command defines computer code.
         
         The \i\c{\\C} command defines a chapter.

       Halibut will treat these terms as the same, and will fold the two
       sets of references into one combined list (although it will warn
       you that it is doing this). The idea is to ensure that people who
       forget to use `\ii' find out about it rather than Halibut silently
       generating a bad index; checking an index for errors is very hard
       work, so Halibut tries to avoid errors in the first place as much as
       it can.

       If you do come across this situation, you will need to define two
       distinguishable index terms. What I did in this manual was something
       like this:

         The \i\c{\\c} command defines computer code.
         
         The \I{\\C-upper}\c{\\C} command defines a chapter.
         
         \IM{\\C-upper} \c{\\C}

       The effect of this will be two separate index entries, one reading
       `\c' and the other reading `\C', pointing to the right places.

   3.6 Configuring Halibut

       Halibut uses the `\cfg' command to allow you to configure various
       aspects of its functionality.

       The `\cfg' command expects to be followed by at least one pair
       of braces, and usually more after that. The first pair of braces
       contains a keyword indicating what aspect of Halibut you want to
       configure, and the meaning of the one(s) after that depends on the
       first keyword.

       Each output format supports a range of configuration options of its
       own (and some configuration is shared between similar output formats
       - the PDF and PostScript formats share most of their configuration,
       as described in section 4.7). The configuration keywords for each
       output format are listed in the manual section for that format; see
       chapter 4.

       There are also a small number of configuration options which apply
       across all output formats:

       \cfg{chapter}{_new chapter name_}

           This tells Halibut that you don't want to call a chapter
           a chapter any more. For example, if you give the command
           \cfg{chapter}{Book}, then any chapter defined with the `\C'
           command will be labelled `Book' rather than `Chapter', both in
           the section headings and in cross-references. This is probably
           most useful if your document is not written in English.

           Your replacement name should be given with a capital letter.
           Halibut will leave it alone if it appears at the start of a
           sentence (in a chapter title, or when `\K' is used), and will
           lower-case it otherwise (when `\k' is used).

       \cfg{section}{_new section name_}

           Exactly like `chapter', but changes the name given to
           subsections of a chapter.

       \cfg{appendix}{_new appendix name_}

           Exactly like `chapter', but changes the name given to
           appendices.

       \cfg{contents}{_new contents name_}

           This changes the name given to the contents section (by default
           `Contents') in back ends which generate one.

       \cfg{index}{_new index name_}

           This changes the name given to the index section (by default
           `Index') in back ends which generate one.

       \cfg{input-charset}{_character set name_}

           This tells Halibut what character set you are writing your input
           file in. By default, it is assumed to be US-ASCII (meaning
           _only_ plain ASCII, with no accented characters at all).

           You can specify any well-known name for any supported character
           set. For example, `iso-8859-1', `iso8859-1' and `iso_8859-1' are
           all recognised, `GB2312' and `EUC-CN' both work, and so on. (You
           can list character sets known to Halibut with by invoking it
           with the --list-charsets option; see section 2.1.)

           This directive takes effect immediately after the `\cfg'
           command. All text after that until the end of the input file is
           expected to be in the new character set. You can even change
           character set several times within a file if you really want to.

           When Halibut reads the input file, everything you type will be
           converted into Unicode from the character set you specify here,
           will be processed as Unicode by Halibut internally, and will be
           written to the various output formats in whatever character sets
           they deem appropriate.

       \cfg{quotes}{_open-quote_}{_close-quote_}[{_open-quote_}{_close-
       quote_...}]

           This specifies the quote characters which should be used. You
           should separately specify the open and close quote marks; each
           quote mark can be one character (\cfg{quotes}{`}{'}), or more
           than one (\cfg{quotes}{<<}{>>}).

           \cfg{quotes} can be overridden by configuration directives for
           each individual backend (see chapter 4); it is a convenient way
           of setting quote characters for all backends at once.

           All backends use these characters in response to the `\q'
           command (see section 3.2.3). Some (such as the text backend) use
           them for other purposes too.

           You can specify multiple fallback options in this command (a
           pair of open and close quotes, each in their own braces, then
           another pair, then another if you like), and Halibut will choose
           the first pair which the output character set supports (Halibut
           will always use a matching pair). (This is to allow you to
           configure quote characters once, generate output in several
           different character sets, and have Halibut constantly adapt to
           make the best use of the current encoding.) For example, you
           might write

             \cfg{quotes}{\u201c}{\u201d}{"}{"}

           and Halibut would use the Unicode matched double quote
           characters if possible, and fall back to ASCII double quotes
           otherwise. If the output character set were to contain U+201C
           but not U+201D, then Halibut would fall back to using the ASCII
           double quote character as _both_ open and close quotes. (No
           known character set is that silly; I mention it only as an
           example.)

           \cfg{quotes} (and the backend-specific versions) apply to the
           _entire_ output; it's not possible to change quote characters
           partway through the output.

       In addition to these configuration commands, there are also
       configuration commands provided by each individual output format.
       These configuration commands are discussed along with each output
       format, in chapter 4.

       The default settings for the above options are:

         \cfg{chapter}{Chapter}
         \cfg{section}{Section}
         \cfg{appendix}{Appendix}
         \cfg{contents}{Contents}
         \cfg{index}{Index}
         \cfg{input-charset}{ASCII}

       The default for \cfg{input-charset} can be changed with the --
       input-charset option; see section 2.1. The default settings for
       \cfg{quotes} are backend-specific; see chapter 4.

   3.7 Defining macros

       If there's a complicated piece of Halibut source which you think
       you're going to use a lot, you can define your own Halibut command
       to produce that piece of source.

       In section 3.2.7, there is a sample piece of code which prints
       a Euro sign, or replaces it with `EUR' if the Euro sign is not
       available:

         This is likely to cost \u20AC{EUR\_}2500 at least.

       If your document quotes a _lot_ of prices in Euros, you might not
       want to spend all your time typing that out. So you could define a
       macro, using the `\define' command:

         \define{eur} \u20AC{EUR\_}

       Your macro names may include Roman alphabetic characters (`a'-`z',
       `A'-`Z') and ordinary Arabic numerals (`0'-`9'), but nothing else.
       (This is general syntax for all of Halibut's commands, except for
       a few special ones such as `\_' and `\-' which consist of a single
       punctuation character only.)

       Then you can just write ...

         This is likely to cost \eur 2500 at least.

       ... except that that's not terribly good, because you end up with
       a space between the Euro sign and the number. (If you had written
       `\eur2500', Halibut would have tried to interpret it as a macro
       command called `eur2500', which you didn't define.) In this case,
       it's helpful to use the special `\.' command, which is defined to do
       nothing at all! But it acts as a separator between your macro and
       the next character:

         This is likely to cost \eur\.2500 at least.

       This way, you will see no space between the Euro sign and the
       number (although, of course, there will be space between `EUR' and
       the number if the Euro sign is not available, because the macro
       definition specifically asked for it).

Chapter 4: Halibut output formats
---------------------------------

       This chapter describes each of Halibut's current output formats. It
       gives some general information about the format, and also describes
       all the configuration directives which are specific to that format.

   4.1 Plain text

       This output format generates the document as a single plain text
       file. No table of contents or index is generated.

       The precise formatting of the text file can be controlled by
       a variety of configuration directives. They are listed in the
       following subsections.

 4.1.1 Output file name

       \cfg{text-filename}{_filename_}

           Sets the output file name in which to store the text file. This
           directive is implicitly generated if you provide a file name
           parameter after the command-line option `--text' (see section
           2.1).

 4.1.2 Indentation and line width

       This section describes the configuration directives which control
       the horizontal dimensions of the output text file: how much
       paragraphs are indented by and how long the lines are.

       \cfg{text-width}{_width_}

           Sets the width of the main part of the document, in characters.
           This width will be used for wrapping paragraphs and for centring
           titles (if you have asked for titles to be centred - see section
           4.1.3). This width does _not_ include the left indentation set
           by \cfg{text-indent}; if you specify an indent of 8 and a width
           of 64, your maximum output line length will be 72.

       \cfg{text-indent}{_indent_}

           Sets the left indentation for the document. If you set this to
           zero, your document will look like an ordinary text file as
           someone with a text editor might have written it; if you set it
           above zero, the text file will have a margin down the left in
           the style of some printed manuals, and you can then configure
           the section numbers to appear in this margin (see section
           4.1.3).

       \cfg{text-indent-code}{_indent_}

           Specifies how many extra characters of indentation (on top of
           the normal left indent) should be given to  code paragraphs.

       \cfg{text-list-indent}{_indent_}

           Specifies how many extra spaces should be used to indent the
           bullet or number in a bulletted or numbered list. The actual
           body of the list item will be indented by this much _plus_ the
           value configured by \cfg{text-listitem-indent}.

       \cfg{text-listitem-indent}{_indent_}

           Specifies how many extra spaces should be used to indent the
           body of a list item, over and above the number configured in
           \cfg{text-list-indent}.

       \cfg{text-indent-preamble}{_boolean_}

           When this is set to `true', the document preamble (i.e. any
           paragraphs appearing before the first chapter heading) will be
           indented to the level specified by \cfg{text-indent}. If this
           setting is `false', the document preamble will not be indented
           at all from the left margin.

 4.1.3 Configuring heading display

       The directives in this section allow you to configure the appearance
       of the title, chapter and section headings in your text file.

       Several of the directives listed below specify the alignment of a
       heading. These alignment options have three possible values:

       `left'

           Align the heading to the very left of the text file (column
           zero).

       `leftplus'

           Align the section title to the left of the main display region
           (in other words, indented to the level specified by \cfg{text-
           indent}). The section _number_ is placed to the left of that (so
           that it goes in the margin if there is room).

       `centre'

           Centre the heading.

       Also, several of the directives below specify how a title should
       be underlined. The parameter to one of these directives should be
       either blank ({}) or a piece of text which will be repeated to
       produce the underline. So you might want to specify, for example,
       \text-title-underline{=} but \text-chapter-underline{-}.

       You can also specify more than one underline setting, and Halibut
       will choose the first one that the output character set supports.
       So, for example, you could write \text-chapter-underline{\u203e}{-},
       and Halibut would use the Unicode `OVERLINE' character where
       possible and fall back to the ASCII minus sign otherwise.

       \cfg{text-title-align}{_alignment_}

           Specifies the alignment of the overall document title: `left',
           `leftplus' or `centre'.

       \cfg{text-title-underline}{_underline-text_}

           Specifies how the overall document title should be underlined.

       \cfg{text-chapter-align}{_alignment_}

           Specifies the alignment of chapter and appendix headings.

       \cfg{text-chapter-underline}{_underline-text_}

           Specifies how chapter and appendix headings should be
           underlined.

       \cfg{text-chapter-numeric}{_boolean_}

           If this is set to `true', then chapter headings will not contain
           the word `Chapter' (or whatever other word you have defined in
           its place - see section 3.3.5 and section 3.6); they will just
           contain the chapter _number_, followed by the chapter title. If
           you set this to `false', chapter headings will be prefixed by
           `Chapter' or equivalent.

       \cfg{text-chapter-shownumber}{_boolean_}

           If this is set to `false', then chapter headings will _only_
           contain the chapter title: they will not contain the word
           `Chapter' (or whatever other word you have defined in its
           place), and neither will they contain the chapter number. If set
           to `false', this overrides \cfg{text-chapter-numeric}.

       \cfg{text-chapter-suffix}{_text_}

           This specifies the suffix text to be appended to the chapter
           number, before displaying the chapter title. For example, if you
           set this to `: ', then the chapter title might look something
           like `Chapter 2: Doing Things'.

       \cfg{text-section-align}{_level_}{_alignment_}

           Specifies the alignment of section headings at a particular
           level. The _level_ parameter specifies which level of section
           headings you want to affect: 0 means first-level headings
           (`\H'), 1 means second-level headings (`\S'), 2 means the level
           below that (`\S2'), and so on. The _alignment_ parameter is
           treated just like the other alignment directives listed above.

       \cfg{text-section-underline}{_level_}{_underline-text_}

           Specifies how to underline section headings at a particular
           level.

       \cfg{text-section-numeric}{_level_}{_boolean_}

           Specifies whether section headings at a particular level should
           contain the word `Section' or equivalent (if `false'), or should
           be numeric only (if `true').

       \cfg{text-section-shownumber}{_level_}{_boolean_}

           If this is set to `false', then section headings at the
           specified level will _only_ contain the section title: they will
           not contain the word `Section' (or whatever other word you have
           defined in its place), and neither will they contain the section
           number. If set to `false', this overrides \cfg{text-section-
           numeric}.

       \cfg{text-section-suffix}{_level_}{_text_}

           Specifies the suffix text to be appended to section numbers at a
           particular level, before displaying the section title.

 4.1.4 Configuring the characters used

       \cfg{text-charset}{_character set name_}

           This tells Halibut what character set the output should be in.
           Any Unicode characters representable in this set will be output
           verbatim; any other characters will not be output and their
           fallback text (if any) will be used instead.

           The character set names are the same as for \cfg{input-charset}
           (see section 3.6). However, unlike \cfg{input-charset}, this
           directive affects the _entire_ output; it's not possible to
           switch encodings halfway through.

       \cfg{text-bullet}{_text_}[{_text_...}]

           This specifies the text which should be used as the bullet in
           bulletted lists. It can be one character (\cfg{text-bullet}{-}),
           or more than one (\cfg{text-bullet}{(*)}).

           Like \cfg{quotes} (see section 3.6), you can specify multiple
           possible options after this command, and Halibut will choose
           the first one which the output character set supports. For
           example, you might write \cfg{text-bullet}{\u2022}{\u00b7}{*},
           in which case Halibut would use the Unicode `BULLET' character
           where possible, fall back to the ISO-8859-1 `MIDDLE DOT' if that
           wasn't available, and resort to the ASCII asterisk if all else
           failed.

       \cfg{text-rule}{_text_}[{_text_...}]

           This specifies the text which should be used for drawing
           horizontal rules (generated by `\rule'; see section 3.3.3). It
           can be one character, or more than one. The string you specify
           will be repeated to reach the required width, so you can specify
           something like `-=' to get a rule that looks like -=-=-=.

           Like \cfg{text-bullet}, you can specify multiple fallback
           options in this command.

       \cfg{text-quotes}{_open-quote_}{_close-quote_}[{_open-
       quote_}{_close-quote_...}]

           This specifies a set of quote characters for the text backend,
           overriding any defined by \cfg{quotes}. It has the same syntax
           (see section 3.6).

           In this backend, these quotes will also be used to mark text
           enclosed in the `\c' command (see section 3.2.2).

       \cfg{text-emphasis}{_start-emph_}{_end-emph_}[{_start-emph_}{_end-
       emph_...}]

           This specifies the characters which should be used to surround
           emphasised text (written using the `\e' command; see section
           3.2.1).

       \cfg{text-strong}{_start-strong_}{_end-strong_}[{_start-
       strong_}{_end-strong_...}]

           This specifies the characters which should be used to surround
           strong text (written using the `\s' command; see section 3.2.1).

           You should separately specify the start-emphasis and end-
           emphasis text, each of which can be more than one character if
           you want. Also, like \cfg{text-quotes}, you can specify multiple
           pairs of fallback options in this command, and Halibut will
           always use a matching pair.

 4.1.5 Miscellaneous configuration options

       \cfg{text-list-suffix}{_text_}

           This text is appended to the number on a numbered list item (see
           section 3.3.2.2). So if you want to label your lists as `1)',
           `2)' and so on, then you would write \cfg{text-list-suffix}{)}.

       \cfg{text-versionid}{_boolean_}

           If this is set to `true', version ID paragraphs (defined using
           the `\versionid' command - see section 3.3.6) will be included
           at the bottom of the text file. If it is set to `false', they
           will be omitted completely.

 4.1.6 Default settings

       The default settings for Halibut's plain text output format are:

         \cfg{text-filename}{output.txt}
         
         \cfg{text-width}{68}
         \cfg{text-indent}{7}
         \cfg{text-indent-code}{2}
         \cfg{text-list-indent}{1}
         \cfg{text-listitem-indent}{3}
         \cfg{text-indent-preamble}{false}
         
         \cfg{text-title-align}{centre}
         \cfg{text-title-underline}{\u2550}{=}
         
         \cfg{text-chapter-align}{left}
         \cfg{text-chapter-underline}{\u203e}{-}
         \cfg{text-chapter-numeric}{false}
         \cfg{text-chapter-shownumber}{true}
         \cfg{text-chapter-suffix}{: }
         
         \cfg{text-section-align}{0}{leftplus}
         \cfg{text-section-underline}{0}{}
         \cfg{text-section-numeric}{0}{true}
         \cfg{text-section-shownumber}{0}{true}
         \cfg{text-section-suffix}{0}{ }
         
         \cfg{text-section-align}{1}{leftplus}
         \cfg{text-section-underline}{1}{}
         \cfg{text-section-numeric}{1}{true}
         \cfg{text-section-shownumber}{1}{true}
         \cfg{text-section-suffix}{1}{ }
         
         ... and so on for all section levels below this ...
         
         \cfg{text-charset}{ASCII}
         \cfg{text-bullet}{\u2022}{-}
         \cfg{text-rule}{\u2500}{-}
         \cfg{text-quotes}{\u2018}{\u2019}{`}{'}
         \cfg{text-emphasis}{_}{_}
         
         \cfg{text-list-suffix}{.}
         \cfg{text-versionid}{true}

   4.2 HTML

       This output format generates an HTML version of the document.
       By default, this will be in multiple files, starting with
       `Contents.html' and splitting the document into files by chapter
       and/or subsection. You can configure precisely how the text is split
       between HTML files using the configuration commands described in
       this section. In particular, you can configure Halibut to output one
       single HTML file instead of multiple ones.

       Configuration directives with an `xhtml-' prefix are synonyms for
       those with an `html-' prefix.

 4.2.1 Controlling the output file names

       \cfg{html-contents-filename}{_filename_}

           Sets the output file name in which to store the top-level
           contents page. Since this is the first page a user ought to see
           when beginning to read the document, a good choice in many cases
           might be `index.html' (although this is not the default, for
           historical reasons).

       \cfg{html-index-filename}{_filename_}

           Sets the file name in which to store the document's index.

       \cfg{html-template-filename}{_template_}

           Provides a template to be used when constructing the file names
           of each chapter or section of the document. This template should
           contain at least one _formatting command_, in the form of a per
           cent sign followed by a letter. (If you need a literal per cent
           sign, you can write `%%'.)

           The formatting commands used in this template are:

           `%N'

               Expands to the visible title of the section, with
               white space removed. So in a chapter declared as
               `\C{fish} Catching Fish', this formatting command would
               expand to `CatchingFish'.

           `%n'

               Expands to the type and number of the section, without white
               space. So in chapter 1 this would expand to `Chapter1'; in
               section A.4.3 it would expand to `SectionA.4.3', and so on.
               If the section has no number (an unnumbered chapter created
               using `\U'), this directive falls back to doing the same
               thing as `%N'.

           `%b'

               Expands to the number of the section, in a format suitable
               for an HTML fragment name. The first character of the
               section type is prepended to the section number. So in
               chapter 1 this would expand to `C1'; in section A.4.3 it
               would expand to `SA.4.3', and so on. If the section has no
               number (an unnumbered chapter created using `\U'), this
               directive falls back to doing the same thing as `%N'.

           `%k'

               Expands to the internal keyword specified in the section
               title. So in a chapter declared as `\C{fish} Catching Fish',
               this formatting command would expand to `fish'. If the
               section has no keyword (an unnumbered chapter created using
               `\U'), this directive falls back to doing the same thing as
               `%N'.

           These formatting directives can also be used in the \cfg{html-
           template-fragment} configuration directive (see section 4.2.7).

       \cfg{html-single-filename}{_filename_}

           Sets the file name in which to store the entire document, if
           Halibut is configured (using `\cfg{html-leaf-level}{0}') to
           produce a single self-contained file. Both this directive _and_
           `\cfg{html-leaf-level}{0}' are implicitly generated if you
           provide a file name parameter after the command-line option `--
           html' (see section 2.1).

 4.2.2 Controlling the splitting into HTML files

       By default, the HTML output from Halibut is split into multiple
       files. Each file typically contains a single chapter or section
       and everything below it, unless subsections of that chapter are
       themselves split off into further files.

       Most files also contain a contents section, giving hyperlinks to the
       sections in the file and/or the sections below it.

       The configuration directives listed below allow you to configure the
       splitting into files, and the details of the contents sections.

       \cfg{html-leaf-level}{_depth_}

           This setting indicates the depth of section which should be
           given a `leaf' file (a file with no sub-files). So if you set it
           to 1, for example, then every chapter will be given its own HTML
           file, plus a top-level contents file. If you set this to 2, then
           each chapter _and_ each `\H' section will have a file, and the
           chapter files will mostly just contain links to their sub-files.

           If you set this option to zero, then the whole document will
           appear in a single file. If you do this, Halibut will call that
           file `Manual.html' instead of `Contents.html' by default.

           This option is automatically set to zero if you provide a file
           name parameter after the command-line option `--html' (see
           section 2.1), because you have specified a single file name and
           so Halibut assumes you want the whole document to be placed in
           that file.

           You can also specify the special name `infinity' (or `infinite'
           or `inf') if you want to ensure that _every_ section and
           subsection ends up in a separate file no matter how deep you go.

       \cfg{html-contents-depth}{_level_}{_depth_}

           This directive allows you to specify how deep any contents
           section in a particular level of file should go.

           The _level_ parameter indicates which level of contents section
           you are dealing with. 0 denotes the main contents section in the
           topmost file `Contents.html'; 1 denotes a contents section in
           a chapter file; 2 is a contents section in a file containing a
           `\H' heading, and so on.

           The _depth_ parameter indicates the maximum depth of heading
           which will be shown in this contents section. Again, 1 denotes a
           chapter, 2 is a `\H' heading, 3 is a `\S' heading, and so on.

           So, for example: \cfg{html-contents-depth}{1}{3} instructs
           Halibut to put contents links in chapter files for all sections
           down to `\S' level, but not to go into any more detail than
           that.

           For backwards compatibility, the alternative syntax \cfg{html-
           contents-depth-_level_}{_depth_} is also supported.

       \cfg{html-leaf-contains-contents}{_boolean_}

           If you set this to `true', then each leaf file will contain its
           own contents section which summarises the text within it.

       \cfg{html-leaf-smallest-contents}{_number_}

           Contents sections in leaf files are not output at all if they
           contain very few entries (on the assumption that it just isn't
           worth bothering). This directive configures the minimum number
           of entries required in a leaf contents section to make Halibut
           bother generating it at all.

 4.2.3 Including pieces of your own HTML

       The directives in this section allow you to supply pieces of
       verbatim HTML code, which will be included in various parts of the
       output files.

       Note that none of Halibut's usual character set translation is
       applied to this code; it is assumed to already be in a suitable
       encoding for the target HTML files.

       \cfg{html-head-end}{_HTML text_}

           The text you provide in this directive is placed at the end of
           the <HEAD> section of each output HTML file. So this is a good
           place to put, for example, a link to a CSS stylesheet.

       \cfg{html-local-head}{_HTML text_}

           This configuration directive is local: you specify it within a
           document section, and it acts on that section only.

           The text you provide in this directive is placed at the end of
           the <HEAD> section of whichever output HTML file contains the
           section in which the directive was placed. You can specify this
           directive multiple times in multiple sections if you like.

           This directive is particularly useful for constructing MacOS
           on-line help, which is mostly normal HTML but which requires a
           special <META NAME="AppleTitle"> tag in the topmost source file.
           You can arrange this by placing this configuration directive in
           the preamble or the introduction section, something like this:

             \cfg{html-local-head}{<meta name="AppleTitle"
             content="MyApp Help">}

       \cfg{html-body-tag}{_HTML text_}

           The text you provide in this directive is used in place of the
           <BODY> tag in each output file. So if you wanted to define a
           background colour, for example, you could write \cfg{html-body-
           tag}{<body bg="#123456">}.

       \cfg{html-body-start}{_HTML text_}

           The text you provide in this directive is placed at the
           beginning of the <BODY> section of each output HTML file. So
           if you intend your HTML files to be part of a web site with a
           standard house style, and the style needs a header at the top of
           every page, this is where you can add that header.

       \cfg{html-body-end}{_HTML text_}

           The text you provide in this directive is placed at the end of
           the <BODY> section of each output HTML file, before any address
           section. So if you intend your HTML files to be part of a web
           site with a standard house style, and the style needs a footer
           at the bottom of every page, this is where you can add that
           footer.

       \cfg{html-address-start}{_HTML text_}

           The text you provide in this directive is placed at the
           beginning of the <ADDRESS> section at the bottom of each output
           HTML file. This might be a good place to put authors' contact
           details, for example.

       \cfg{html-address-end}{_HTML text_}

           The text you provide in this directive is placed at the end of
           the <ADDRESS> section at the bottom of each output HTML file,
           after the version IDs (if present).

       \cfg{html-navigation-attributes}{_HTML attributes_}

           The text you provide in this directive is included inside the
           <P> tag containing the navigation links at the top of each
           page (`Previous' / `Contents' / `Next'). So if you wanted the
           navigation links to have a particular CSS style, you could
           write \cfg{html-navigation-attributes}{class="foo"}, and the
           navigation-links paragraph would then begin with the tag
           <p class="foo">.

 4.2.4 Configuring heading display

       \cfg{html-chapter-numeric}{_boolean_}

           If this is set to `true', then chapter headings will not contain
           the word `Chapter' (or whatever other word you have defined in
           its place - see section 3.3.5 and section 3.6); they will just
           contain the chapter _number_, followed by the chapter title. If
           you set this to `false', chapter headings will be prefixed by
           `Chapter' or equivalent.

       \cfg{html-chapter-shownumber}{_boolean_}

           If this is set to `false', then chapter headings will _only_
           contain the chapter title: they will not contain the word
           `Chapter' (or whatever other word you have defined in its
           place), and neither will they contain the chapter number. If set
           to `false', this overrides \cfg{html-chapter-numeric}.

       \cfg{html-chapter-suffix}{_text_}

           This specifies the suffix text to be appended to the chapter
           number, before displaying the chapter title. For example, if you
           set this to `: ', then the chapter title might look something
           like `Chapter 2: Doing Things'.

       \cfg{html-section-numeric}{_level_}{_boolean_}

           Specifies whether section headings at a particular level should
           contain the word `Section' or equivalent (if `false'), or should
           be numeric only (if `true'). The _level_ parameter specifies
           which level of section headings you want to affect: 0 means
           first-level headings (`\H'), 1 means second-level headings
           (`\S'), 2 means the level below that (`\S2'), and so on.

       \cfg{html-section-shownumber}{_level_}{_boolean_}

           If this is set to `false', then section headings at the
           specified level will _only_ contain the section title: they will
           not contain the word `Section' (or whatever other word you have
           defined in its place), and neither will they contain the section
           number. If set to `false', this overrides \cfg{html-section-
           numeric}.

       \cfg{html-section-suffix}{_level_}{_text_}

           Specifies the suffix text to be appended to section numbers at a
           particular level, before displaying the section title.

 4.2.5 Configuring standard text

       These directives let you fine-tune the names Halibut uses in
       places such as the navigation bar to refer to various parts of the
       document, and other standard pieces of text, for instance to change
       them to a different language.

       \cfg{html-preamble-text}{_text_}

       \cfg{html-contents-text}{_text_}

       \cfg{html-index-text}{_text_}

           Text used to refer to the preamble (i.e., any paragraphs before
           the first chapter heading), contents, and index respectively, in
           the navigation bar, contents, and index.

           (`html-contents-text' and `html-index-text' override the cross-
           format configuration keywords `contents' and `index' (see
           section 3.6, if both appear. They are legacy keywords preserved
           for backwards compatibility; you should generally use `contents'
           and `index'.)

       \cfg{html-title-separator}{_text_}

           If multiple headings are used in a file's <TITLE> tag, this text
           is used to separate them.

       \cfg{html-index-main-separator}{_text_}

           Separator between index term and references in the index.

       \cfg{html-index-multiple-separator}{_text_}

           Separator between multiple references for a single index term in
           the index.

       \cfg{html-pre-versionid}{_text_}

       \cfg{html-post-versionid}{_text_}

           Text surrounding each output version ID paragraph.

       \cfg{html-nav-prev-text}{_text_}

       \cfg{html-nav-next-text}{_text_}

       \cfg{html-nav-up-text}{_text_}

           The text used for the `previous page', `next page', and `up'
           links on the navigation bar.

       \cfg{html-nav-separator}{_text_}

           Separator between links in the navigation bar.

 4.2.6 Configuring the characters used

       Unlike the other backends, HTML does not have a single \cfg{html-
       charset} directive, as there are several levels of character
       encoding to consider.

       The character set names are the same as for \cfg{input-charset} (see
       section 3.6). However, unlike \cfg{input-charset}, these directives
       affect the _entire_ output; it's not possible to switch encodings
       halfway through.

       \cfg{html-output-charset}{_character set name_}

           The character encoding of the HTML file to be output. Unicode
           characters in this encoding's repertoire are included literally
           rather than as HTML entities.

       \cfg{html-restrict-charset}{_character set name_}

           Only Unicode characters representable in this character set will
           be output; any others will be omitted and use their fallback
           text, if any. Characters not in `html-output-charset' will be
           represented as HTML numeric entities.

       \cfg{html-quotes}{_open-quote_}{_close-quote_}[{_open-
       quote_}{_close-quote_...}]

           Specifies the quotation marks to use, overriding any
           \cfg{quotes} directive. You can specify multiple fallback
           options. Works exactly like the \cfg{text-quotes} directive (see
           section 4.1.4).

 4.2.7 Miscellaneous options

       \cfg{html-version}{_version_}

           Identifies the precise version of HTML that is output. This
           affects the declaration within the HTML, and also has minor
           effects on the body of the HTML so that it is valid for the
           declared version. The available variants are:

           html3.2

               W3C HTML 3.2

           html4

               W3C HTML 4.01 Strict

           iso-html

               ISO/IEC 15445:2000

           xhtml1.0transitional

               W3C XHTML 1.0 Transitional

           xhtml1.0strict

               W3C XHTML 1.0 Strict

       \cfg{html-template-fragment}{_template_}[{_template_}{...}]

           This directive lets you specify a template, with exactly the
           same syntax used in \cfg{html-template-filename} (see section
           4.2.1), to be used for the anchor names (<A NAME="...">) used
           to allow URLs to refer to specific sections within a particular
           HTML file. So if you set this to `%k', for example, then each
           individual section in your document will be addressable by means
           of a URL ending in a `#' followed by your internal section
           keyword.

           If more than one template is specified, anchors are generated in
           all the specified formats; Halibut's own cross-references are
           generated with the first template.

           Characters that are not permitted in anchor names are stripped.
           If there are no valid characters left, or a fragment is non-
           unique, Halibut starts inventing fragment names and suffixes as
           appropriate.

           Note that there are potentially fragment names that are not
           controlled by this mechanism, such as index references.

       \cfg{html-versionid}{_boolean_}

           If this is set to `true', version ID paragraphs (defined using
           the `\versionid' command - see section 3.3.6) will be included
           visibly in the <ADDRESS> section at the bottom of each HTML
           file. If it is set to `false', they will only be included as
           HTML comments.

       \cfg{html-rellinks}{_boolean_}

           If this is set to `true', machine-readable relational links will
           be emitted in each HTML file (<LINK REL="next"> and so on within
           the <HEAD> section) providing links to related files. The same
           set of links are provided as in the navigation bar (with which
           this should not be confused).

           Some browsers make use of this semantic information, for
           instance to allow easy navigation through related pages, and to
           prefetch the next page. (Search engines can also make use of
           it.) However, many browsers ignore this markup, so it would be
           unwise to rely on it for navigation.

           The use and rendering of this information is entirely up to the
           browser; none of the other Halibut options for the navigation
           bar will have any effect.

       \cfg{html-suppress-navlinks}{_boolean_}

           If this is set to `true', the usual navigation links within the
           _body_ of each HTML file (near the top of the rendered page)
           will be suppressed.

       \cfg{html-suppress-address}{_boolean_}

           If this is set to `true', the <ADDRESS> section at the bottom of
           each HTML file will be omitted completely. (This will therefore
           also cause version IDs not to be included visibly.)

       \cfg{html-author}{_text_}

           The text supplied here goes in a <META name="author"> tag in
           the output HTML files, so that browsers which support this can
           automatically identify the author of the document.

       \cfg{html-description}{_text_}

           The text supplied here goes in a <META name="description"> tag
           in the output HTML files, so that browsers which support this
           can easily pick out a brief description of the document.

 4.2.8 Default settings

       The default settings for Halibut's HTML output format are:

         \cfg{html-contents-filename}{Contents.html}
         \cfg{html-index-filename}{IndexPage.html}
         \cfg{html-template-filename}{%n.html}
         \cfg{html-single-filename}{Manual.html}
         
         \cfg{html-leaf-level}{2}
         \cfg{html-leaf-contains-contents}{false}
         \cfg{html-leaf-smallest-contents}{4}
         \cfg{html-contents-depth}{0}{2}
         \cfg{html-contents-depth}{1}{3}
         ... and so on for all section levels below this ...
         
         \cfg{html-head-end}{}
         \cfg{html-body-tag}{<body>}
         \cfg{html-body-start}{}
         \cfg{html-body-end}{}
         \cfg{html-address-start}{}
         \cfg{html-address-end}{}
         \cfg{html-navigation-attributes}{}
         
         \cfg{html-chapter-numeric}{false}
         \cfg{html-chapter-shownumber}{true}
         \cfg{html-chapter-suffix}{: }
         
         \cfg{html-section-numeric}{0}{true}
         \cfg{html-section-shownumber}{0}{true}
         \cfg{html-section-suffix}{0}{ }
         
         \cfg{html-section-numeric}{1}{true}
         \cfg{html-section-shownumber}{1}{true}
         \cfg{html-section-suffix}{1}{ }
         
         ... and so on for all section levels below this ...
         
         \cfg{html-preamble-text}{Preamble}
         \cfg{html-contents-text}{Contents}
         \cfg{html-index-text}{Index}
         \cfg{html-title-separator}{ - }
         \cfg{html-index-main-separator}{: }
         \cfg{html-index-multiple-separator}{, }
         \cfg{html-pre-versionid}{[}
         \cfg{html-post-versionid}{]}
         \cfg{html-nav-prev-text}{Previous}
         \cfg{html-nav-next-text}{Next}
         \cfg{html-nav-up-text}{Up}
         \cfg{html-nav-separator}{ | }
         
         \cfg{html-output-charset}{ASCII}
         \cfg{html-restrict-charset}{UTF-8}
         \cfg{html-quotes}{\u2018}{\u2019}{"}{"}
         
         \cfg{html-version}{html4}
         \cfg{html-template-fragment}{%b}
         \cfg{html-versionid}{true}
         \cfg{html-rellinks}{true}
         \cfg{html-suppress-navlinks{false}
         \cfg{html-suppress-address}{false}
         \cfg{html-author}{}
         \cfg{html-description}{}

   4.3 Windows HTML Help

       This output format generates a `.chm' file suitable for use with the
       Windows HTML Help system.

       Older versions of Halibut could only generate HTML Help by writing
       out a set of source files acceptable to the MS help compiler.
       Nowadays Halibut can generate CHM directly, so that's no longer
       necessary. However, the legacy method is still available if you need
       it; see section 4.3.6 for details.

 4.3.1 Output file name

       \cfg{chm-filename}{_filename_}

           Sets the output file name in which to store the HTML Help
           file. This directive is implicitly generated if you provide a
           file name parameter after the command-line option `--chm' (see
           section 2.1).

 4.3.2 Configuration shared with the HTML back end

       As the name suggests, an HTML Help file is mostly a compressed
       container for HTML files. So the CHM back end shares a great deal of
       its code with the HTML back end, and as a result, it supports the
       same range of format configuration options.

       (One exception to this general rule is that the configuration
       options relating to generating _HTML Help compiler input_ are
       not supported in CHM mode, because they wouldn't make any sense!
       The html-mshtmlhelp-* options described in section 4.3.6 have no
       analogue starting chm-.)

       However, because HTML and CHM are used in different ways, you
       may need to configure the two back ends differently. So in CHM
       mode, Halibut supports all the same configuration directives
       described in section 4.2, but with their names changed so that
       they begin with `chm-' in place of `html-'. This lets you maintain
       two sets of configuration independently; for example, you could
       specify `\cfg{html-chapter-numeric}{true}' and `\cfg{chm-chapter-
       numeric}{false}' in the same source file, and then when you ran
       Halibut with both the `--html' and `--chm' options, it would produce
       purely numeric chapter titles in the HTML output but not in the CHM
       file.

       If you do decide to apply a piece of configuration across both these
       back ends, you can prefix it with `htmlall-' instead of `html-' or
       `chm-'. For example, `\cfg{htmlall-chapter-numeric}{true}' will
       enable purely numeric chapter titles in _both_ the HTML and CHM
       output.

 4.3.3 Including extra files in the CHM

       CHM files are mostly a container for HTML, and the HTML files inside
       them are allowed to cross-refer to all the usual other kinds of
       file that HTML might refer to, such as images, stylesheets and even
       Javascript. If you want to make use of this capability, you need to
       tell Halibut what extra files it needs to incorporate into the CHM
       container.

       \cfg{chm-extra-file}{_filename_}

       \cfg{chm-extra-file}{_filename_}{_name inside CHM_}

           Tells Halibut to read an additional input file from _filename_
           and incorporate it into the CHM.

           In the first form of the directive, the file will be given the
           same name within the CHM's internal namespace (i.e. for the
           purposes of linking to it from HTML files) as Halibut used
           to load it from disk. If you need to include the file with a
           different internal name, you can use the second form of the
           directive, which separately specifies the name under which
           Halibut should look for the input file and the name it should
           give it inside the CHM.

           You can specify this directive multiple times, to include more
           than one file.

 4.3.4 Renaming the CHM internal support files

       As well as ordinary HTML, there are also two special files inside
       a CHM, containing the table of contents and the index. Halibut
       generates these automatically, and you normally don't have to worry
       about them. However, it is _just_ possible (though very unlikely!)
       that you might find they conflict with the name of some file you
       wanted to include in the CHM yourself, and hence, Halibut provides
       configuration options to change them if you need to.

       \cfg{chm-contents-name}{_filename_}

           Controls the name of the internal contents file in the CHM.

       \cfg{chm-index-name}{_filename_}

           Controls the name of the internal index file in the CHM.

 4.3.5 Default settings

       The default settings for Halibut's CHM output format are mostly the
       same as for the standard HTML output. However, a few defaults are
       changed to be more in line with the way CHM wants to do things.

         \cfg{chm-filename}{output.chm}
         \cfg{chm-contents-name}{contents.hhc}
         \cfg{chm-index-name}{index.hhk}
         \cfg{chm-leaf-level}{infinite}
         \cfg{chm-suppress-navlinks{true}
         \cfg{chm-suppress-address}{true}

 4.3.6 Generating input to the MS Windows HTML Help compiler

       Before Halibut gained the ability to write out CHM files directly,
       it used a more cumbersome system in which you could run it in HTML
       mode and enable some extra options that would write out supporting
       files needed by the official Windows HTML Help compiler, so that you
       could still generate a CHM file from your Halibut source in multiple
       build steps.

       This legacy system for HTML Help generation is still supported,
       partly to avoid backwards-compatibility breakage for anyone already
       using it, and also because it permits more flexibility in the
       resulting CHM files: Halibut's own CHM file generation makes some
       fixed decisions about window layout and styling, whereas if you use
       the official help compiler you can start from Halibut's default
       project file and make whatever manual changes you like to that sort
       of thing.

       To enable the generation of MS HTML Help auxiliary files, use the
       following configuration directives:

       \cfg{html-mshtmlhelp-project}{_filename_}

           Instructs Halibut to output an HTML Help project file with the
           specified name. You will almost certainly want the filename
           to end in the extension `.hhp' (although Halibut will not
           enforce this). If you use this option, you must also use the
           html-mshtmlhelp-chm option to specify the desired name of the
           compiled help file.

       \cfg{html-mshtmlhelp-chm}{_filename_}

           Specifies the desired name of the compiled HTML Help file. You
           will almost certainly want this to have the extension `.chm'
           (although Halibut will not enforce this). The name you specify
           here will be written into the help project file. If you specify
           this option, you must also use the html-mshtmlhelp-project
           option to request a help project file in the first place.

       \cfg{html-mshtmlhelp-contents}{_filename_}

           Instructs Halibut to output an HTML Help contents file with the
           specified name, and refer to it in the help project file. You
           will almost certainly want the filename to end in the extension
           `.hhc' (although Halibut will not enforce this). This option
           will be ignored if you have not also specified a help project
           file.

           Creating a contents file like this causes the HTML Help viewer
           to display a contents tree in the pane to the left of the main
           text window. You can choose to generate an HTML Help project
           without this feature, in which case the user will still be able
           to navigate around the document by using the ordinary internal
           links in the HTML files themselves just as if it were a web
           page. However, using a contents file is recommended.

       \cfg{html-mshtmlhelp-index}{_filename_}

           Instructs Halibut to output an HTML Help index file with the
           specified name, and refer to it in the help project file. You
           will almost certainly want the filename to end in the extension
           `.hhk' (although Halibut will not enforce this). This option
           will be ignored if you have not also specified a help project
           file.

           Specifying this option suppresses the generation of an HTML-
           based index file (see \cfg{html-index-filename} in section
           4.2.1).

           Creating an index file like this causes the HTML Help viewer to
           provide a list of index terms in a pane to the left of the main
           text window. You can choose to generate an HTML Help project
           without this feature, in which case a conventional HTML index
           will be generated instead (assuming you have any index terms
           at all defined) and the user will still be able to use that.
           However, using an index file is recommended.

           Halibut will not output an index file at all, or link to one
           from the help project file, if your document contains no index
           entries.

       If you use the above options, Halibut will output a help project
       file which you should be able to feed straight to the command-
       line MS HTML Help compiler (HHC.EXE), or load into the MS HTML Help
       Workshop (HHW.EXE).

       You may also wish to alter other HTML configuration options to make
       the resulting help file look more like a help file and less like a
       web page. If you use Halibut's direct CHM output, this is done for
       you automatically (see section 4.3.5); but if you're using the HTML
       output mode then I recommend the following changes.

        -  \cfg{html-leaf-level}{infinite}, because HTML Help works best
           with lots of small files (`topics') rather than a few large
           ones. In particular, the contents and index mechanisms can only
           reference files, not subsections within files.

        -  \cfg{html-suppress-navlinks}{true}, because HTML Help has
           its own navigation facilities and it looks a bit strange to
           duplicate them.

        -  \cfg{html-suppress-address}{true}, because the <ADDRESS> section
           makes less sense in a help file than it does on a web page.

   4.4 Legacy Windows Help

       This output format generates data that can be used by the legacy
       Windows Help program WINHLP32.EXE. There are two actual files
       generated, one ending in `.hlp' and the other ending in `.cnt'.

       This legacy Windows Help format was discontinued in 2006 in favour
       of HTML Help, which Halibut can also generate. You probably want
       to use that instead for any new project. See section 4.3 for more
       information on this.

       Currently, the Windows Help output is hardcoded to be in the
       `Win1252' character set. (If anyone knows how character sets are
       encoded in Windows Help files, we'd appreciate help.)

       The Windows Help output format supports the following configuration
       directives:

 4.4.1 Output file name

       \cfg{winhelp-filename}{_filename_}

           Sets the output file name in which to store the help file. This
           directive is implicitly generated if you provide a file name
           parameter after the command-line option `--winhelp' (see section
           2.1).

           Your output file name should end with `.hlp'; if it doesn't,
           Halibut will append it. Halibut will also generate a contents
           file (ending in `.cnt') alongside the file name you specify.

 4.4.2 Configuring the characters used

       \cfg{winhelp-bullet}{_text_}[{_text_}...]

           Specifies the text to use as the bullet in bulletted lists. You
           can specify multiple fallback options. Works exactly like the
           \cfg{text-bullet} directive (see section 4.1.4).

       \cfg{winhelp-quotes}{_open-quote_}{_close-quote_}[{_open-
       quote_}{_close-quote_...}]

           Specifies the quotation marks to use, overriding any
           \cfg{quotes} directive. You can specify multiple fallback
           options. Works exactly like the \cfg{text-quotes} directive (see
           section 4.1.4).

 4.4.3 Miscellaneous configuration options

       \cfg{winhelp-contents-titlepage}{_title_}

           Sets the text used to describe the help page containing the
           blurb (see section 3.3.6) and table of contents.

       \cfg{winhelp-section-suffix}{_text_}

           Specifies the suffix text to be appended to section numbers,
           before displaying the section title. (Applies to all levels.)

       \cfg{winhelp-list-suffix}{_text_}

           This text is appended to the number on a numbered list item,
           in exactly the same way as \cfg{text-list-suffix} (see section
           4.1.4).

       \cfg{winhelp-topic}{_topic-name_}

           This directive defines a Windows Help topic name in the current
           section. Topic names can be used by the program invoking
           WINHELP.EXE to jump straight to a particular section. So you can
           use this for context-sensitive help.

           For example, if you used this directive in a particular section:

             \cfg{winhelp-topic}{savingfiles}

           then a Windows application could invoke Windows Help to jump to
           that particular section in the help file like this:

             WinHelp(hwnd, "mydoc.hlp", HELP_COMMAND,
                     (DWORD)"JI(`',`savingfiles')");

           You can use this configuration directive many times, in many
           different subsections of your document, in order to define a lot
           of different help contexts which you can use in this way.

 4.4.4 Default settings

       The default settings for the Windows Help output format are:

         \cfg{winhelp-filename}{output.hlp}
         
         \cfg{winhelp-bullet}{\u2022}{-}
         \cfg{winhelp-quotes}{\u2018}{\u2019}{"}{"}
         
         \cfg{winhelp-contents-titlepage}{Title page}
         \cfg{winhelp-section-suffix}{: }
         \cfg{winhelp-list-suffix}{.}

       and no `\cfg{winhelp-topic}' directives anywhere.

   4.5 Unix man pages

       This output format generates a Unix man page. That is to say, it
       generates `nroff' input designed to work with the `-mandoc' macro
       package.

       The available configuration options for this format are as follows:

 4.5.1 Output file name

       \cfg{man-filename}{_filename_}

           Sets the output file name in which to store the man page. This
           directive is implicitly generated if you provide a file name
           parameter after the command-line option `--man' (see section
           2.1).

 4.5.2 Configuring headers and footers

       \cfg{man-identity}{_text_}{_text..._}

           This directive is used to generate the initial `.TH' directive
           that appears at the top of a man page. It expects to be followed
           by some number of brace pairs containing text, which will be
           used in the headers and footers of the formatted output.

           A traditional order for the arguments appears to be:

            1. The name of the program.

            2. The (numeric) manual section.

            3. The date that the man page was written.

            4. The name of any containing suite of which the program is a
               part.

            5. The name of the author of the man page.

           For example, a typical man page might contain

             \cfg{man-identity}{make-foo}{1}{June 2003}{foo-utils}{Fred
             Bloggs}

 4.5.3 Configuring heading display

       \cfg{man-headnumbers}{_boolean_}

           If this is set to `true', then section headings in the man page
           will have their section numbers displayed as usual. If set
           to `false', the section numbers will be omitted. (man pages
           traditionally have section names such as `SYNOPSIS', `OPTIONS'
           and `BUGS', and do not typically number them, so `false' is the
           setting which conforms most closely to normal man style.)

       \cfg{man-mindepth}{_depth_}

           If this is set to a number greater than 0, then section headings
           _higher_ than the given depth will not be displayed. If it is
           set to zero, all section headings will be displayed as normal.

           The point of this is so that you can use the same Halibut input
           file to generate a quick-reference man page for a program, _and_
           to include that man page as an appendix in your program's full
           manual. If you are to include the man page as an appendix, then
           the internal headings within the page will probably need to be
           at `\H' or `\S' level; therefore, when you format that input
           file on its own to create the man page itself, you will need
           to have defined a `\C' and possibly a `\H' heading beforehand,
           which you don't want to see displayed.

           Here's an example. You might have a file `appendix.but', which
           simply says

             \A{manpages} \cw{man} pages for the Foo tool suite
             
             \cfg{man-mindepth}{2}

           Then you have a file `make-foo.but', and probably others like it
           as well, each of which looks something like this:

             \cfg{man-identity}{make-foo}{1}{June 2003}{foo-utils}{Fred
             Bloggs}
             
             \H{man-foo} \cw{man} page for \c{make-foo}
             
             \S{man-foo-name} NAME
             
             \c{make-foo} - create Foo files for the Foo tool suite
             
             \S{man-foo-synopsis} SYNOPSIS
             
             ... and so on ...

           So when you're generating your main manual, you can include
           `appendix.but' followed by `make-foo.but' and any other man
           pages you have, and your man pages will be formatted neatly as
           part of an appendix. Then, in a separate run of Halibut, you can
           just do

             halibut appendix.but make-foo.but

           and this will generate a man page `output.1', in which the
           headings `man pages for the Foo tool suite' and `man page for
           `make-foo'' will not be displayed because of the `man-mindepth'
           directive. So the first visible heading in the output man page
           will be `NAME', exactly as a user would expect.

 4.5.4 Configuring the characters used

       \cfg{man-charset}{_character set_}

           Specifies what character set the output should be in, similarly
           to \cfg{text-charset} (see section 4.1.4).

       \cfg{man-bullet}{_text_}[{_text_}...]

           Specifies the text to use as the bullet in bulletted lists. You
           can specify multiple fallback options. Works exactly like the
           \cfg{text-bullet} directive (see section 4.1.4).

       \cfg{man-rule}{_text_}[{_text_...}]

           This specifies the text which should be used for drawing
           horizontal rules (generated by `\rule'; see section 3.3.3) when
           the manual page is rendered into text. It should only be one
           character long, but otherwise it works like the \cfg{text-rule}
           directive (see section 4.1.4).

       \cfg{man-quotes}{_open-quote_}{_close-quote_}[{_open-quote_}{_close-
       quote_...}]

           Specifies the quotation marks to use, overriding any
           \cfg{quotes} directive. You can specify multiple fallback
           options. Works exactly like the \cfg{text-quotes} directive (see
           section 4.1.4).

 4.5.5 Default settings

       The default settings for the man page output format are:

         \cfg{man-filename}{output.1}
         
         \cfg{man-identity}{}
         
         \cfg{man-headnumbers}{false}
         \cfg{man-mindepth}{0}
         
         \cfg{man-charset}{ASCII}
         \cfg{man-bullet}{\u2022}{o}
         \cfg{man-rule}{\u2500}{-}
         \cfg{man-quotes}{\u2018}{\u2019}{"}{"}

   4.6 GNU Info

       This output format generates files which can be used with the GNU
       Info program.

       There are typically multiple output files: a primary file whose
       name usually ends in `.info', and one or more subsidiary files
       whose names have numbers on the end, so that they end in `.info-
       1', `.info-2' and so on. Alternatively, this output format can
       be configured to output a single large file containing the whole
       document.

       The Info output format supports the following configuration
       directives:

 4.6.1 Controlling the output filenames

       \cfg{info-filename}{_filename_}

           Sets the output file name in which to store the Info file. This
           directive is implicitly generated if you provide a file name
           parameter after the command-line option `--info' (see section
           2.1).

           The suffixes `-1', `-2', `-3' and so on will be appended to your
           output file name to produce any subsidiary files required.

           Note that Info files refer to their own names internally, so
           these files cannot be renamed after creation and remain useful.

       \cfg{info-max-file-size}{_bytes_}

           Sets the preferred maximum file size for each subsidiary file.
           As a special case, if you set this to zero, there will be no
           subsidiary files and the whole document will be placed in a
           single self-contained output file. (However, note that this file
           can still not be renamed usefully.)

           The preferred maximum file size is only a guideline. Halibut may
           be forced to exceed it if a single section of the document is
           larger than the maximum size (since individual Info nodes may
           not be split between files).

 4.6.2 Indentation and line width

       \cfg{info-width}{_width_}

           Sets the width of the main part of the document, in characters.
           Works exactly like the \cfg{text-width} directive (see section
           4.1.2).

       \cfg{info-indent-code}{_indent_}

           Specifies the extra indentation for  code paragraphs. Works
           exactly like the \cfg{text-indent-code} directive (see section
           4.1.2).

       \cfg{info-index-width}{_width_}

           Specifies how much horizontal space to leave in the index node
           for the text of index terms, before displaying the sections the
           terms occur in.

       \cfg{info-list-indent}{_indent_}

           Specifies the extra indentation before the bullet or number
           in a list item. Works exactly like the \cfg{text-list-indent}
           directive (see section 4.1.2).

       \cfg{info-listitem-indent}{_indent_}

           Specifies the additional indentation before the body of a
           list item. Works exactly like the \cfg{text-listitem-indent}
           directive (see section 4.1.2).

 4.6.3 Configuring heading display

       \cfg{info-section-suffix}{_text_}

           Specifies the suffix text to be appended to each section number
           before displaying the section title. For example, if you set
           this to `: ', then a typical section title might look something
           like `Section 3.1: Something Like This'.

       \cfg{info-title-underline}{_text_}[{_text_}...]

           Specifies the text to be used to underline the overall document
           title. Works very much like the \cfg{text-title-underline}
           directive (see section 4.1.3). You can specify more than one
           option, and Halibut will choose the first one supported by the
           character set.

       \cfg{info-chapter-underline}{_text_}[{_text_}...]

           Specifies how chapter and appendix headings should be
           underlined.

       \cfg{info-section-underline}{_level_}{_text_}[{_text_}...]

           Specifies how to underline section headings at a particular
           level. The _level_ parameter specifies which level of section
           headings you want to affect: 0 means first-level headings
           (`\H'), 1 means second-level headings (`\S'), 2 means the level
           below that (`\S2'), and so on.

 4.6.4 Controlling the characters used

       \cfg{info-charset}{_character set_}

           Specifies what character set the output should be in, similarly
           to \cfg{text-charset} (see section 4.1.4).

       \cfg{info-bullet}{_text_}[{_text_}...]

           Specifies the text to use as the bullet in bulletted lists. You
           can specify multiple fallback options. Works exactly like the
           \cfg{text-bullet} directive (see section 4.1.4).

       \cfg{info-rule}{_text_}[{_text_}...]

           Specifies the text used to draw horizontal rules. You can
           specify multiple fallback options. Works exactly like the
           \cfg{text-rule} directive (see section 4.1.4).

       \cfg{info-quotes}{_open-quote_}{_close-quote_}[{_open-
       quote_}{_close-quote_...}]

           Specifies the quotation marks to use, overriding any
           \cfg{quotes} directive. You can specify multiple fallback
           options. Works exactly like the \cfg{text-quotes} directive (see
           section 4.1.4).

       \cfg{info-emphasis}{_start-emph_}{_end-emph_}[{_start-emph_}{_end-
       emph_...}]

           Specifies how to display emphasised text. You can specify
           multiple fallback options. Works exactly like the \cfg{text-
           emphasis} directive (see section 4.1.4).

       \cfg{info-strong}{_start-strong_}{_end-strong_}[{_start-
       strong_}{_end-strong_...}]

           Specifies how to display strong text. You can specify multiple
           fallback options. Works exactly like the \cfg{text-emphasis}
           directive (see section 4.1.4).

 4.6.5 Miscellaneous configuration options

       \cfg{info-list-suffix}{_text_}

           Specifies the text to append to the item numbers in a numbered
           list. Works exactly like the \cfg{text-list-suffix} directive
           (see section 4.1.5).

       \cfg{info-dir-entry}{_section_}{_short name_}{_long
       name_}[{_keyword_}]

           Constructs an INFO-DIR-ENTRY section and places it in the header
           of the Info file. This mechanism is used to automatically
           generate the `dir' file at the root of a Unix system's Info
           collection.

           The parameters to this directive are:

           _section_

               Specifies the section of the `dir' file in which you want
               your document referenced. For example, `Development', or
               `Games', or `Miscellaneous'.

           _short name_

               Specifies a short name for the directory entry, which will
               appear at the start of the menu line.

           _long name_

               Specifies a long name for the directory entry, which will
               appear at the end of the menu line.

           _keyword_

               This parameter is optional. If it is present, then the
               directory entry will cause a jump to a particular subsection
               of your document, rather than starting at the top. The
               subsection will be the one referred to by the given keyword
               (see section 3.3.5 for details about assigning keywords to
               document sections).

           For example, in a document describing many game programs, the
           configuration directive

             \cfg{info-dir-entry}{Games}{Chess}{Electronic chess
             game}{chess}

           might produce text in the `dir' file looking something like
           this:

             Games
             * Chess: (mygames)Chapter 3.   Electronic chess game

           if the output file were called `mygames.info' and the keyword
           `chess' had been used to define Chapter 3 of the document.

 4.6.6 Default settings

       The default settings for the Info output format are:

         \cfg{info-filename}{output.info}
         \cfg{info-max-file-size}{65536}
         
         \cfg{info-width}{70}
         \cfg{info-indent-code}{2}
         \cfg{info-index-width}{40}
         \cfg{info-list-indent}{1}
         \cfg{info-listitem-indent}{3}
         
         \cfg{info-section-suffix}{: }
         \cfg{info-title-underline}{*}
         \cfg{info-chapter-underline}{=}
         \cfg{info-section-underline}{0}{-}
         \cfg{info-section-underline}{1}{.}
         \cfg{info-section-underline}{2}{.}
         ... and so on for all section levels below this ...
         
         \cfg{info-charset}{ASCII}
         \cfg{info-bullet}{\u2022}{-}
         \cfg{info-rule}{\u2500}{-}
         \cfg{info-quotes}{\u2018}{\u2019}{`}{'}
         \cfg{info-emphasis}{_}{_}
         \cfg{info-strong}{*}{*}
         
         \cfg{info-list-suffix}{.}

       and no \cfg{info-dir-entry} directives.

   4.7 Paper formats

       These output formats (currently PDF and PostScript) generate
       printable manuals. As such, they share a number of configuration
       directives.

 4.7.1 PDF

       This output format generates a printable manual in PDF format.
       In addition, it uses some PDF interactive features to provide
       an outline of all the document's sections and clickable cross-
       references between sections.

       There is one configuration option specific to PDF:

       \cfg{pdf-filename}{_filename_}

           Sets the output file name in which to store the PDF file. This
           directive is implicitly generated if you provide a file name
           parameter after the command-line option `--pdf' (see section
           2.1).

       The default settings for the PDF output format are:

         \cfg{pdf-filename}{output.pdf}

 4.7.2 PostScript

       This output format generates a printable manual in PostScript
       format. This should look exactly identical to the PDF output (see
       section 4.7.2), and uses `pdfmark' to arrange that if converted to
       PDF it will contain the same interactive features.

       There is one configuration option specific to PostScript:

       \cfg{ps-filename}{_filename_}

           Sets the output file name in which to store the PostScript file.
           This directive is implicitly generated if you provide a file
           name parameter after the command-line option `--ps' (see section
           2.1).

       The default settings for the PostScript output format are:

         \cfg{ps-filename}{output.ps}

 4.7.3 Configuring layout and measurements

       All measurements are in PostScript points (72 points to the inch).

4.7.3.1 Page properties

       \cfg{paper-page-width}{_points_}

       \cfg{paper-page-height}{_points_}

           Specify the absolute limits of the paper.

       \cfg{paper-left-margin}{_points_}

       \cfg{paper-top-margin}{_points_}

       \cfg{paper-right-margin}{_points_}

       \cfg{paper-bottom-margin}{_points_}

           Specify the margins. Most text appears within these margins,
           except:

            -  Section numbers, which appear in the left margin.

            -  The footer (containing page numbers), which appears in the
               bottom margin.

4.7.3.2 Vertical spacing

       \cfg{paper-base-leading}{_points_}

           Specifies the amount of space between lines of text within a
           paragraph. (So, if the font size is 12pt and there is 2pt of
           leading, there will be 14pt between successive baselines.)

       \cfg{paper-base-para-spacing}{_points_}

           Specifies the amount of vertical space between paragraphs. (The
           vertical space between paragraphs does _not_ include `paper-
           base-leading'.)

4.7.3.3 Indentation

       \cfg{paper-list-indent}{_points_}

           Specifies the indentation of the bullet or number in a bulletted
           or numbered list, similarly to \cfg{text-list-indent} (see
           section 4.1.2).

       \cfg{paper-listitem-indent}{_points_}

           Specifies the _extra_ indentation for the body of a list item,
           over and above the amount configured in \cfg{paper-list-indent}.

       \cfg{paper-quote-indent}{_points_}

           Specifies the amount of indentation for a level of quoting. Used
           for \quote (see section 3.3.4) and code quotes with \c (see
           section 3.2.2).

4.7.3.4 Headings

       \cfg{paper-chapter-top-space}{_points_}

           Specifies the space between the top margin and the top of the
           chapter heading. (Each chapter begins on a new page.)

       \cfg{paper-chapter-underline-thickness}{_points_}

           Specifies the vertical thickness of the black rule under chapter
           headings.

       \cfg{paper-chapter-underline-depth}{_points_}

           Specifies the distance between the base of the chapter heading
           and the _base_ of the underlying rule.

       \cfg{paper-sect-num-left-space}{_points_}

           Specifies the distance between the left margin and the _right_
           of section numbers (which are in the left margin).

4.7.3.5 Contents and index

       \cfg{paper-contents-indent-step}{_points_}

           Specifies by how much to indent each entry in the table of
           contents per level of subdivision in the document. (In other
           words, chapter titles appear at the left of the table of
           contents, headings within the chapter are indented by the amount
           configured here, subheadings by twice that, and so on.)

       \cfg{paper-contents-margin}{_points_}

           Specifies the amount of space on the right of the table of
           contents which should be reserved for page numbers only.
           Headings in the table of contents which extend into this space
           will be wrapped.

       \cfg{paper-leader-separation}{_points_}

           Specifies the horizontal spacing between dots in _leaders_ (the
           dotted lines that appear between section headings and page
           numbers in the table of contents).

       \cfg{paper-footer-distance}{_points_}

           Specifies the distance between the bottom margin and the _base_
           of the footer (which contains page numbers).

       \cfg{paper-index-columns}{_columns_}

           Specifies the number of columns the index should be divided
           into.

       \cfg{paper-index-gutter}{_points_}

           Specifies the amount of  horizontal space between index columns.

       \cfg{paper-index-minsep}{_points_}

           Specifies the minimum allowable horizontal space between an
           index entry and its page number. If the gap is smaller, the page
           number is moved to the next line.

4.7.3.6 Fonts

       The directives in this section control which fonts Halibut uses for
       various kinds of text. Directives for setting the font normally take
       three font names, the first of which is used for normal text, the
       second for emphasised text, and the third for code. Any fonts which
       aren't specified are left unchanged.

       Halibut intrinsically knows about some fonts, and these fonts are
       also built into all PDF and most PostScript implementations. These
       fonts can be used without further formality. Halibut can also use
       other fonts, and can embed them it its PDF and PostScript output.
       These other fonts are supplied to Halibut by simply adding them to
       the list of input files on its command line.

       To use a Type 1 font Halibut needs both the font file itself, in
       either hexadecimal (PFA) or IBM PC (PFB) format, and an Adobe Font
       Metrics (AFM) file. The AFM file must be specified first on the
       command line. If Halibut gets an AFM file without a corresponding
       Type 1 font file, the PostScript and PDF output files will still use
       that font, but they won't contain it.

       Using a TrueType font is rather simpler, and simply requires you to
       pass the font file to Halibut. Halibut does place a few restrictions
       on TrueType fonts, notably that they must include a Unicode mapping
       table and a PostScript name.

       Fonts are specified using their PostScript names. Running Halibut
       with the --list-fonts option causes it to display the PostScript
       names of all the fonts it intrinsically knows about, along with any
       fonts the were supplied as input files.

       Font sizes are specified in PostScript points (72 to the inch).

       \cfg{paper-title-fonts}{_normal-font_}[{_emph-font_}[{_code-font_}]]

           Specifies the fonts to use for text in the document title.

       \cfg{paper-title-font-size}{_points_}

           Specifies the font size of the document title.

       \cfg{paper-chapter-fonts}{_normal-font_}[{_emph-font_}[{_code-
       font_}]]

           Specifies the fonts to use for text in chapter titles.

       \cfg{paper-chapter-font-size}{_points_}

           Specifies the font size of chapter titles.

       \cfg{paper-section-fonts}{_level_}{_normal-font_}[{_emph-
       font_}[{_code-font_}]]

           Specifies the fonts to use for text in section headings at the
           _level_ specified.

       \cfg{paper-section-font-size}{_level_}{_points_}

           Specifies the font size of section headings at the _level_
           specified.

       \cfg{paper-base-fonts}{_normal-font_}[{_emph-font_}[{_code-font_}]]

           Specifies the fonts to use for text in the body text.

       \cfg{paper-base-font-size}{_points_}

           Specifies the font size of body text.

       \cfg{paper-code-fonts}{_bold-font_}[{_italic-font_}[{_normal-
       font_}]]

           Specifies the fonts to use for text in code paragraphs. The
           _bold-font_ is used for bold text, the _italic-font_ for
           emphasised text, and the _normal-font_ for normal code.

       \cfg{paper-code-font-size}{_points_}

           Specifies the font size of text in code paragraphs.

       \cfg{paper-pagenum-font-size}{_points_}

           Specifies the font size to use for page numbers.

4.7.3.7 Miscellaneous

       \cfg{paper-rule-thickness}{_points_}

           Specifies the vertical thickness of the rule produced by the
           \rule command (see section 3.3.3). (Note that no extra space is
           reserved for thicker rules.)

 4.7.4 Configuring the characters used

       \cfg{paper-bullet}{_text_}[{_text_}...]

           Specifies the text to use as the bullet in bulletted lists. You
           can specify multiple fallback options. Works exactly like the
           \cfg{text-bullet} directive (see section 4.1.4).

       \cfg{paper-quotes}{_open-quote_}{_close-quote_}[{_open-
       quote_}{_close-quote_...}]

           Specifies the quotation marks to use, overriding any
           \cfg{quotes} directive. You can specify multiple fallback
           options. Works exactly like the \cfg{text-quotes} directive (see
           section 4.1.4).

 4.7.5 Default settings for paper formats

       The default page size corresponds to 210 x 297 mm, i.e., A4 paper.

         \cfg{paper-page-width}{595} 
         \cfg{paper-page-height}{842} 
         
         \cfg{paper-left-margin}{72} 
         \cfg{paper-top-margin}{72} 
         \cfg{paper-right-margin}{72} 
         \cfg{paper-bottom-margin}{108} 
         
         \cfg{paper-base-leading}{1} 
         \cfg{paper-base-para-spacing}{10} 
         
         \cfg{paper-list-indent}{6} 
         \cfg{paper-listitem-indent}{18} 
         \cfg{paper-quote-indent}{18} 
         
         \cfg{paper-chapter-top-space}{72} 
         \cfg{paper-chapter-underline-thickness}{3} 
         \cfg{paper-chapter-underline-depth}{14} 
         \cfg{paper-sect-num-left-space}{12} 
         
         \cfg{paper-contents-indent-step}{24} 
         \cfg{paper-contents-margin}{84} 
         \cfg{paper-leader-separation}{12} 
         \cfg{paper-footer-distance}{32} 
         \cfg{paper-index-columns}{2} 
         \cfg{paper-index-gutter}{36} 
         \cfg{paper-index-minsep}{18} 
         
         \cfg{paper-base-fonts}{Times-Roman}{Times-Italic}{Courier}
         \cfg{paper-base-font-size}{12} 
         \cfg{paper-code-fonts}{Courier-Bold}{Courier-Oblique}{Courier}
         \cfg{paper-code-font-size}{12}
         \cfg{paper-title-fonts}{Helvetica-Bold}
             {Helvetica-BoldOblique}{Courier-Bold}
         \cfg{paper-title-font-size}{24}
         \cfg{paper-chapter-fonts}{Helvetica-Bold}
             {Helvetica-BoldOblique}{Courier-Bold}
         \cfg{paper-chapter-font-size}{20}
         \cfg{paper-section-fonts}{0}{Helvetica-Bold}
             {Helvetica-BoldOblique}{Courier-Bold}
         \cfg{paper-section-font-size}{0}{16}
         \cfg{paper-section-fonts}{1}{Helvetica-Bold}
             {Helvetica-BoldOblique}{Courier-Bold}
         \cfg{paper-section-font-size}{1}{14}
         \cfg{paper-section-fonts}{2}{Helvetica-Bold}
             {Helvetica-BoldOblique}{Courier-Bold}
         \cfg{paper-section-font-size}{2}{13}
         ... and so on for all section levels below this ...
         
         \cfg{paper-pagenum-font-size}{12} 
         
         \cfg{paper-rule-thickness}{1} 
         
         \cfg{paper-bullet}{\u2022}{-}
         \cfg{paper-quotes}{\u2018}{\u2019}{'}{'}

Appendix A: Halibut Licence
---------------------------

       Halibut is copyright (c) 1999-2021 Simon Tatham.

       Permission is hereby granted, free of charge, to any person
       obtaining a copy of this software and associated documentation files
       (the "Software"), to deal in the Software without restriction,
       including without limitation the rights to use, copy, modify, merge,
       publish, distribute, sublicense, and/or sell copies of the Software,
       and to permit persons to whom the Software is furnished to do so,
       subject to the following conditions:

       The above copyright notice and this permission notice shall be
       included in all copies or substantial portions of the Software.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
       EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
       OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
       NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
       BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
       ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
       CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
       SOFTWARE.

       Halibut contains font metrics derived from the _Font Metrics for
       PDF Core 14 Fonts_, which carry the following copyright notice and
       licence:

         Copyright (c) 1985, 1987, 1989, 1990, 1991, 1992, 1993, 1997 Adobe
         Systems Incorporated. All Rights Reserved.

         This file and the 14 PostScript(R) AFM files it accompanies may be
         used, copied, and distributed for any purpose and without charge,
         with or without modification, provided that all copyright notices
         are retained; that the AFM files are not distributed without this
         file; that all modifications to this file or any of the AFM files
         are prominently noted in the modified file(s); and that this
         paragraph is not modified. Adobe Systems has no responsibility or
         obligation to support the use of the AFM files.

Appendix B: Halibut man page
----------------------------

   B.1 NAME

       halibut - multi-format documentation formatting tool

   B.2 SYNOPSIS

         halibut [options] file1.but [file2.but ...]

   B.3 DESCRIPTION

       `halibut' reads the given set of input files, assembles them into a
       document, and outputs that document in one or more formats.

       The available command-line options can configure what formats
       Halibut should output in, and can also configure other things about
       the way Halibut works.

   B.4 OPTIONS

       The command-line options supported by `halibut' are:

       --text[=_filename_]

           Makes Halibut generate an output file in plain text format.
           If the optional _filename_ parameter is supplied, the output
           text file will be given that name. Otherwise, the name of the
           output text file will be as specified in the input files, or
           `output.txt' if none is specified at all.

       --html[=_filename_]

           Makes Halibut generate one or more output files in HTML format.
           If the optional _filename_ parameter is supplied, there will be
           precisely one HTML output file with that name, containing the
           whole document. Otherwise, there may be one or more than one
           HTML file produced as output; this, and the file names, will be
           as specified in the input files, or given a set of default names
           starting with `Contents.html' if none is specified at all.

       --chm[=_filename_]

           Makes Halibut generate an output file in Windows HTML Help
           format. If the optional _filename_ parameter is supplied, the
           output help file will be given that name. Otherwise, the name of
           the output help file will be as specified in the input files, or
           `output.chm' if none is specified at all.

       --winhelp[=_filename_]

           Makes Halibut generate an output file in old-style Windows Help
           format. If the optional _filename_ parameter is supplied, the
           output help file will be given that name. Otherwise, the name of
           the output help file will be as specified in the input files, or
           `output.hlp' if none is specified at all.

           The output help file must have a name ending in `.hlp'; if it
           does not, `.hlp' will be added. A secondary contents file will
           be created alongside the main help file, with the same name
           except that it will end in `.cnt' (for example `output.cnt', if
           the main file is `output.hlp').

       --man[=_filename_]

           Makes Halibut generate an output file in Unix man page format.
           If the optional _filename_ parameter is supplied, the output man
           page will be given that name. Otherwise, the name of the output
           man page will be as specified in the input files, or `output.1'
           if none is specified at all.

       --info[=_filename_]

           Makes Halibut generate an `info' file. If the optional
           _filename_ parameter is supplied, the output `info' file will be
           given that name. Otherwise, the name of the output `info' file
           will be as specified in the input files, or `output.info' if
           none is specified at all.

           By default, unless configured otherwise using the \cfg{info-max-
           file-size}{0} directive, the `info' output will be split into
           multiple files. The main file will have the name you specify;
           the subsidiary files will have suffixes `-1', `-2' etc.

       --pdf[=_filename_]

           Makes Halibut generate an output file in PDF format. If the
           optional _filename_ parameter is supplied, the PDF output file
           will be given that name. Otherwise, the name of the output PDF
           file will be as specified in the input files, or `output.pdf' if
           none is specified at all.

       --ps[=_filename_]

           Makes Halibut generate an output file in PostScript format. If
           the optional _filename_ parameter is supplied, the PostScript
           output file will be given that name. Otherwise, the name of the
           output PostScript file will be as specified in the input files,
           or `output.ps' if none is specified at all.

       -C_word_:_word_[:_word_...]

           Adds a configuration directive to the input processed by
           Halibut. Using this directive is exactly equivalent to appending
           an extra input file to the command line which contains the
           directive \cfg{_word_}{_word_}{_word_...}.

       --input-charset=_charset_

           Changes the assumed character set for input files from the
           default of ASCII.

       --list-charsets

           Makes Halibut list character sets known to it.

       --list-fonts

           Makes Halibut list fonts known to it, either intrinsically or by
           being passed as input files.

       --precise

           Makes Halibut report the column number as well as the line
           number when it encounters an error in an input file.

       --help

           Makes Halibut display a brief summary of its command-line
           options.

       --version

           Makes Halibut report its version number.

       --licence

           Makes Halibut display its licence (MIT).

   B.5 MORE INFORMATION

       For more information on Halibut, including full details of the input
       file format, look in the full manual. If this is not installed
       locally on your system, you can also find it at the Halibut web
       site:

       https://www.chiark.greenend.org.uk/~sgtatham/halibut/

   B.6 BUGS

       This man page isn't terribly complete.

[Halibut version 1.3]
