    module Text.Pandoc.Readers.DocBook ( readDocBook ) where
    import Data.Char (toUpper)
    import Text.Pandoc.Shared (safeRead)
    import Text.Pandoc.Options
    import Text.Pandoc.Definition
    import Text.Pandoc.Builder
    import Text.XML.Light
    import Text.Pandoc.Compat.TagSoupEntity (lookupEntity)
    import Data.Either (rights)
    import Data.Generics
    import Data.Char (isSpace)
    import Control.Monad.State
    import Data.List (intersperse)
    import Data.Maybe (fromMaybe)
    import Text.TeXMath (readMathML, writeTeX)
    import Text.Pandoc.Error (PandocError)
    import Text.Pandoc.Compat.Except
    import Data.Default
    import Data.Foldable (asum)

    {-

    List of all DocBook tags, with [x] indicating implemented,
    [o] meaning intentionally left unimplemented (pass through):

    [o] abbrev - An abbreviation, especially one followed by a period
    [x] abstract - A summary
    [o] accel - A graphical user interface (GUI) keyboard shortcut
    [x] ackno - Acknowledgements in an Article
    [o] acronym - An often pronounceable word made from the initial
    [o] action - A response to a user event
    [o] address - A real-world address, generally a postal address
    [ ] affiliation - The institutional affiliation of an individual
    [ ] alt - Text representation for a graphical element
    [o] anchor - A spot in the document
    [x] answer - An answer to a question posed in a QandASet
    [x] appendix - An appendix in a Book or Article
    [x] appendixinfo - Meta-information for an Appendix
    [o] application - The name of a software program
    [x] area - A region defined for a Callout in a graphic or code example
    [x] areaset - A set of related areas in a graphic or code example
    [x] areaspec - A collection of regions in a graphic or code example
    [ ] arg - An argument in a CmdSynopsis
    [x] article - An article
    [x] articleinfo - Meta-information for an Article
    [ ] artpagenums - The page numbers of an article as published
    [x] attribution - The source of a block quote or epigraph
    [ ] audiodata - Pointer to external audio data
    [ ] audioobject - A wrapper for audio data and its associated meta-information
    [x] author - The name of an individual author
    [ ] authorblurb - A short description or note about an author
    [x] authorgroup - Wrapper for author information when a document has
        multiple authors or collabarators
    [x] authorinitials - The initials or other short identifier for an author
    [o] beginpage - The location of a page break in a print version of the document
    [ ] bibliocoverage - The spatial or temporal coverage of a document
    [x] bibliodiv - A section of a Bibliography
    [x] biblioentry - An entry in a Bibliography
    [x] bibliography - A bibliography
    [ ] bibliographyinfo - Meta-information for a Bibliography
    [ ] biblioid - An identifier for a document
    [o] bibliolist - A wrapper for a set of bibliography entries
    [ ] bibliomisc - Untyped bibliographic information
    [x] bibliomixed - An entry in a Bibliography
    [ ] bibliomset - A cooked container for related bibliographic information
    [ ] biblioref - A cross reference to a bibliographic entry
    [ ] bibliorelation - The relationship of a document to another
    [ ] biblioset - A raw container for related bibliographic information
    [ ] bibliosource - The source of a document
    [ ] blockinfo - Meta-information for a block element
    [x] blockquote - A quotation set off from the main text
    [x] book - A book
    [x] bookinfo - Meta-information for a Book
    [x] bridgehead - A free-floating heading
    [x] callout - A “called out” description of a marked Area
    [x] calloutlist - A list of Callouts
    [x] caption - A caption
    [x] caution - A note of caution
    [x] chapter - A chapter, as of a book
    [x] chapterinfo - Meta-information for a Chapter
    [ ] citation - An inline bibliographic reference to another published work
    [ ] citebiblioid - A citation of a bibliographic identifier
    [ ] citerefentry - A citation to a reference page
    [ ] citetitle - The title of a cited work
    [ ] city - The name of a city in an address
    [x] classname - The name of a class, in the object-oriented programming sense
    [ ] classsynopsis - The syntax summary for a class definition
    [ ] classsynopsisinfo - Information supplementing the contents of
        a ClassSynopsis
    [ ] cmdsynopsis - A syntax summary for a software command
    [ ] co - The location of a callout embedded in text
    [x] code - An inline code fragment
    [x] col - Specifications for a column in an HTML table
    [x] colgroup - A group of columns in an HTML table
    [ ] collab - Identifies a collaborator
    [ ] collabname - The name of a collaborator
    [ ] colophon - Text at the back of a book describing facts about its production
    [x] colspec - Specifications for a column in a table
    [x] command - The name of an executable program or other software command
    [x] computeroutput - Data, generally text, displayed or presented by a computer
    [ ] confdates - The dates of a conference for which a document was written
    [ ] confgroup - A wrapper for document meta-information about a conference
    [ ] confnum - An identifier, frequently numerical, associated with a conference for which a document was written
    [ ] confsponsor - The sponsor of a conference for which a document was written
    [ ] conftitle - The title of a conference for which a document was written
    [x] constant - A programming or system constant
    [ ] constraint - A constraint in an EBNF production
    [ ] constraintdef - The definition of a constraint in an EBNF production
    [ ] constructorsynopsis - A syntax summary for a constructor
    [ ] contractnum - The contract number of a document
    [ ] contractsponsor - The sponsor of a contract
    [ ] contrib - A summary of the contributions made to a document by a
        credited source
    [ ] copyright - Copyright information about a document
    [ ] coref - A cross reference to a co
    [ ] corpauthor - A corporate author, as opposed to an individual
    [ ] corpcredit - A corporation or organization credited in a document
    [ ] corpname - The name of a corporation
    [ ] country - The name of a country
    [ ] database - The name of a database, or part of a database
    [x] date - The date of publication or revision of a document
    [ ] dedication - A wrapper for the dedication section of a book
    [ ] destructorsynopsis - A syntax summary for a destructor
    [ ] edition - The name or number of an edition of a document
    [ ] editor - The name of the editor of a document
    [x] email - An email address
    [x] emphasis - Emphasized text
    [x] entry - A cell in a table
    [ ] entrytbl - A subtable appearing in place of an Entry in a table
    [ ] envar - A software environment variable
    [x] epigraph - A short inscription at the beginning of a document or component
        note:  also handle embedded attribution tag
    [x] equation - A displayed mathematical equation
    [ ] errorcode - An error code
    [ ] errorname - An error name
    [ ] errortext - An error message.
    [ ] errortype - The classification of an error message
    [ ] example - A formal example, with a title
    [ ] exceptionname - The name of an exception
    [ ] fax - A fax number
    [ ] fieldsynopsis - The name of a field in a class definition
    [x] figure - A formal figure, generally an illustration, with a title
    [x] filename - The name of a file
    [ ] firstname - The first name of a person
    [ ] firstterm - The first occurrence of a term
    [x] footnote - A footnote
    [ ] footnoteref - A cross reference to a footnote (a footnote mark)
    [x] foreignphrase - A word or phrase in a language other than the primary
        language of the document
    [x] formalpara - A paragraph with a title
    [ ] funcdef - A function (subroutine) name and its return type
    [ ] funcparams - Parameters for a function referenced through a function
        pointer in a synopsis
    [ ] funcprototype - The prototype of a function
    [ ] funcsynopsis - The syntax summary for a function definition
    [ ] funcsynopsisinfo - Information supplementing the FuncDefs of a FuncSynopsis
    [x] function - The name of a function or subroutine, as in a
        programming language
    [x] glossary - A glossary
    [x] glossaryinfo - Meta-information for a Glossary
    [x] glossdef - A definition in a GlossEntry
    [x] glossdiv - A division in a Glossary
    [x] glossentry - An entry in a Glossary or GlossList
    [x] glosslist - A wrapper for a set of GlossEntrys
    [x] glosssee - A cross-reference from one GlossEntry to another
    [x] glossseealso - A cross-reference from one GlossEntry to another
    [x] glossterm - A glossary term
    [ ] graphic - A displayed graphical object (not an inline)
        Note: in DocBook v5 `graphic` is discarded
    [ ] graphicco - A graphic that contains callout areas
        Note: in DocBook v5 `graphicco` is discarded
    [ ] group - A group of elements in a CmdSynopsis
    [ ] guibutton - The text on a button in a GUI
    [ ] guiicon - Graphic and/or text appearing as a icon in a GUI
    [ ] guilabel - The text of a label in a GUI
    [x] guimenu - The name of a menu in a GUI
    [x] guimenuitem - The name of a terminal menu item in a GUI
    [x] guisubmenu - The name of a submenu in a GUI
    [ ] hardware - A physical part of a computer system
    [ ] highlights - A summary of the main points of the discussed component
    [ ] holder - The name of the individual or organization that holds a copyright
    [o] honorific - The title of a person
    [ ] html:form - An HTML form
    [x] imagedata - Pointer to external image data (only `fileref` attribute
        implemented but not `entityref` which would require parsing of the DTD)
    [x] imageobject - A wrapper for image data and its associated meta-information
    [ ] imageobjectco - A wrapper for an image object with callouts
    [x] important - An admonition set off from the text
    [x] index - An index
    [x] indexdiv - A division in an index
    [x] indexentry - An entry in an index
    [x] indexinfo - Meta-information for an Index
    [x] indexterm - A wrapper for terms to be indexed
    [x] info - A wrapper for information about a component or other block. (DocBook v5)
    [x] informalequation - A displayed mathematical equation without a title
    [x] informalexample - A displayed example without a title
    [ ] informalfigure - A untitled figure
    [ ] informaltable - A table without a title
    [ ] initializer - The initializer for a FieldSynopsis
    [x] inlineequation - A mathematical equation or expression occurring inline
    [ ] inlinegraphic - An object containing or pointing to graphical data
        that will be rendered inline
    [x] inlinemediaobject - An inline media object (video, audio, image, and so on)
    [ ] interface - An element of a GUI
    [ ] interfacename - The name of an interface
    [ ] invpartnumber - An inventory part number
    [ ] isbn - The International Standard Book Number of a document
    [ ] issn - The International Standard Serial Number of a periodical
    [ ] issuenum - The number of an issue of a journal
    [x] itemizedlist - A list in which each entry is marked with a bullet or
        other dingbat
    [ ] itermset - A set of index terms in the meta-information of a document
    [ ] jobtitle - The title of an individual in an organization
    [x] keycap - The text printed on a key on a keyboard
    [ ] keycode - The internal, frequently numeric, identifier for a key
        on a keyboard
    [x] keycombo - A combination of input actions
    [ ] keysym - The symbolic name of a key on a keyboard
    [ ] keyword - One of a set of keywords describing the content of a document
    [ ] keywordset - A set of keywords describing the content of a document
    [ ] label - A label on a Question or Answer
    [ ] legalnotice - A statement of legal obligations or requirements
    [ ] lhs - The left-hand side of an EBNF production
    [ ] lineage - The portion of a person's name indicating a relationship to
        ancestors
    [ ] lineannotation - A comment on a line in a verbatim listing
    [x] link - A hypertext link
    [x] listitem - A wrapper for the elements of a list item
    [x] literal - Inline text that is some literal value
    [x] literallayout - A block of text in which line breaks and white space are
        to be reproduced faithfully
    [ ] lot - A list of the titles of formal objects (as tables or figures) in
        a document
    [ ] lotentry - An entry in a list of titles
    [ ] manvolnum - A reference volume number
    [x] markup - A string of formatting markup in text that is to be
        represented literally
    [ ] mathphrase - A mathematical phrase, an expression that can be represented
        with ordinary text and a small amount of markup
    [ ] medialabel - A name that identifies the physical medium on which some
        information resides
    [x] mediaobject - A displayed media object (video, audio, image, etc.)
    [ ] mediaobjectco - A media object that contains callouts
    [x] member - An element of a simple list
    [x] menuchoice - A selection or series of selections from a menu
    [ ] methodname - The name of a method
    [ ] methodparam - Parameters to a method
    [ ] methodsynopsis - A syntax summary for a method
    [x] mml:math - A MathML equation
    [ ] modespec - Application-specific information necessary for the
        completion of an OLink
    [ ] modifier - Modifiers in a synopsis
    [ ] mousebutton - The conventional name of a mouse button
    [ ] msg - A message in a message set
    [ ] msgaud - The audience to which a message in a message set is relevant
    [ ] msgentry - A wrapper for an entry in a message set
    [ ] msgexplan - Explanatory material relating to a message in a message set
    [ ] msginfo - Information about a message in a message set
    [ ] msglevel - The level of importance or severity of a message in a message set
    [ ] msgmain - The primary component of a message in a message set
    [ ] msgorig - The origin of a message in a message set
    [ ] msgrel - A related component of a message in a message set
    [ ] msgset - A detailed set of messages, usually error messages
    [ ] msgsub - A subcomponent of a message in a message set
    [ ] msgtext - The actual text of a message component in a message set
    [ ] nonterminal - A non-terminal in an EBNF production
    [x] note - A message set off from the text
    [ ] objectinfo - Meta-information for an object
    [ ] olink - A link that addresses its target indirectly, through an entity
    [ ] ooclass - A class in an object-oriented programming language
    [ ] ooexception - An exception in an object-oriented programming language
    [ ] oointerface - An interface in an object-oriented programming language
    [x] option - An option for a software command
    [x] optional - Optional information
    [x] orderedlist - A list in which each entry is marked with a sequentially
        incremented label
    [ ] orgdiv - A division of an organization
    [ ] orgname - The name of an organization other than a corporation
    [ ] otheraddr - Uncategorized information in address
    [ ] othercredit - A person or entity, other than an author or editor,
        credited in a document
    [ ] othername - A component of a persons name that is not a first name,
        surname, or lineage
    [ ] package - A package
    [ ] pagenums - The numbers of the pages in a book, for use in a bibliographic
        entry
    [x] para - A paragraph
    [ ] paramdef - Information about a function parameter in a programming language
    [x] parameter - A value or a symbolic reference to a value
    [ ] part - A division in a book
    [ ] partinfo - Meta-information for a Part
    [ ] partintro - An introduction to the contents of a part
    [ ] personblurb - A short description or note about a person
    [ ] personname - The personal name of an individual
    [ ] phone - A telephone number
    [ ] phrase - A span of text
    [ ] pob - A post office box in an address
    [ ] postcode - A postal code in an address
    [x] preface - Introductory matter preceding the first chapter of a book
    [ ] prefaceinfo - Meta-information for a Preface
    [ ] primary - The primary word or phrase under which an index term should be
        sorted
    [ ] primaryie - A primary term in an index entry, not in the text
    [ ] printhistory - The printing history of a document
    [ ] procedure - A list of operations to be performed in a well-defined sequence
    [ ] production - A production in a set of EBNF productions
    [ ] productionrecap - A cross-reference to an EBNF production
    [ ] productionset - A set of EBNF productions
    [ ] productname - The formal name of a product
    [ ] productnumber - A number assigned to a product
    [x] programlisting - A literal listing of all or part of a program
    [ ] programlistingco - A program listing with associated areas used in callouts
    [x] prompt - A character or string indicating the start of an input field in
        a computer display
    [ ] property - A unit of data associated with some part of a computer system
    [ ] pubdate - The date of publication of a document
    [ ] publisher - The publisher of a document
    [ ] publishername - The name of the publisher of a document
    [ ] pubsnumber - A number assigned to a publication other than an ISBN or ISSN
        or inventory part number
    [x] qandadiv - A titled division in a QandASet
    [o] qandaentry - A question/answer set within a QandASet
    [o] qandaset - A question-and-answer set
    [x] question - A question in a QandASet
    [x] quote - An inline quotation
    [ ] refclass - The scope or other indication of applicability of a
        reference entry
    [ ] refdescriptor - A description of the topic of a reference page
    [ ] refentry - A reference page (originally a UNIX man-style reference page)
    [ ] refentryinfo - Meta-information for a Refentry
    [ ] refentrytitle - The title of a reference page
    [ ] reference - A collection of reference entries
    [ ] referenceinfo - Meta-information for a Reference
    [ ] refmeta - Meta-information for a reference entry
    [ ] refmiscinfo - Meta-information for a reference entry other than the title
        and volume number
    [ ] refname - The name of (one of) the subject(s) of a reference page
    [ ] refnamediv - The name, purpose, and classification of a reference page
    [ ] refpurpose - A short (one sentence) synopsis of the topic of a reference
        page
    [x] refsect1 - A major subsection of a reference entry
    [x] refsect1info - Meta-information for a RefSect1
    [x] refsect2 - A subsection of a RefSect1
    [x] refsect2info - Meta-information for a RefSect2
    [x] refsect3 - A subsection of a RefSect2
    [x] refsect3info - Meta-information for a RefSect3
    [x] refsection - A recursive section in a refentry
    [x] refsectioninfo - Meta-information for a refsection
    [ ] refsynopsisdiv - A syntactic synopsis of the subject of the reference page
    [ ] refsynopsisdivinfo - Meta-information for a RefSynopsisDiv
    [x] releaseinfo - Information about a particular release of a document
    [ ] remark - A remark (or comment) intended for presentation in a draft
        manuscript
    [ ] replaceable - Content that may or must be replaced by the user
    [ ] returnvalue - The value returned by a function
    [ ] revdescription - A extended description of a revision to a document
    [ ] revhistory - A history of the revisions to a document
    [ ] revision - An entry describing a single revision in the history of the
        revisions to a document
    [ ] revnumber - A document revision number
    [ ] revremark - A description of a revision to a document
    [ ] rhs - The right-hand side of an EBNF production
    [x] row - A row in a table
    [ ] sbr - An explicit line break in a command synopsis
    [x] screen - Text that a user sees or might see on a computer screen
    [o] screenco - A screen with associated areas used in callouts
    [o] screeninfo - Information about how a screen shot was produced
    [ ] screenshot - A representation of what the user sees or might see on a
        computer screen
    [ ] secondary - A secondary word or phrase in an index term
    [ ] secondaryie - A secondary term in an index entry, rather than in the text
    [x] sect1 - A top-level section of document
    [x] sect1info - Meta-information for a Sect1
    [x] sect2 - A subsection within a Sect1
    [x] sect2info - Meta-information for a Sect2
    [x] sect3 - A subsection within a Sect2
    [x] sect3info - Meta-information for a Sect3
    [x] sect4 - A subsection within a Sect3
    [x] sect4info - Meta-information for a Sect4
    [x] sect5 - A subsection within a Sect4
    [x] sect5info - Meta-information for a Sect5
    [x] section - A recursive section
    [x] sectioninfo - Meta-information for a recursive section
    [x] see - Part of an index term directing the reader instead to another entry
        in the index
    [x] seealso - Part of an index term directing the reader also to another entry
        in the index
    [ ] seealsoie - A See also entry in an index, rather than in the text
    [ ] seeie - A See entry in an index, rather than in the text
    [x] seg - An element of a list item in a segmented list
    [x] seglistitem - A list item in a segmented list
    [x] segmentedlist - A segmented list, a list of sets of elements
    [x] segtitle - The title of an element of a list item in a segmented list
    [ ] seriesvolnums - Numbers of the volumes in a series of books
    [ ] set - A collection of books
    [ ] setindex - An index to a set of books
    [ ] setindexinfo - Meta-information for a SetIndex
    [ ] setinfo - Meta-information for a Set
    [ ] sgmltag - A component of SGML markup
    [ ] shortaffil - A brief description of an affiliation
    [ ] shortcut - A key combination for an action that is also accessible through
        a menu
    [ ] sidebar - A portion of a document that is isolated from the main
        narrative flow
    [ ] sidebarinfo - Meta-information for a Sidebar
    [x] simpara - A paragraph that contains only text and inline markup, no block
        elements
    [x] simplelist - An undecorated list of single words or short phrases
    [ ] simplemsgentry - A wrapper for a simpler entry in a message set
    [ ] simplesect - A section of a document with no subdivisions
    [ ] spanspec - Formatting information for a spanned column in a table
    [ ] state - A state or province in an address
    [ ] step - A unit of action in a procedure
    [ ] stepalternatives - Alternative steps in a procedure
    [ ] street - A street address in an address
    [ ] structfield - A field in a structure (in the programming language sense)
    [ ] structname - The name of a structure (in the programming language sense)
    [ ] subject - One of a group of terms describing the subject matter of a
        document
    [ ] subjectset - A set of terms describing the subject matter of a document
    [ ] subjectterm - A term in a group of terms describing the subject matter of
        a document
    [x] subscript - A subscript (as in H2O, the molecular formula for water)
    [ ] substeps - A wrapper for steps that occur within steps in a procedure
    [x] subtitle - The subtitle of a document
    [x] superscript - A superscript (as in x2, the mathematical notation for x
        multiplied by itself)
    [ ] surname - A family name; in western cultures the last name
    [ ] svg:svg - An SVG graphic
    [x] symbol - A name that is replaced by a value before processing
    [ ] synopfragment - A portion of a CmdSynopsis broken out from the main body
        of the synopsis
    [ ] synopfragmentref - A reference to a fragment of a command synopsis
    [ ] synopsis - A general-purpose element for representing the syntax of
        commands or functions
    [ ] systemitem - A system-related item or term
    [ ] table - A formal table in a document
    [ ] task - A task to be completed
    [ ] taskprerequisites - The prerequisites for a task
    [ ] taskrelated - Information related to a task
    [ ] tasksummary - A summary of a task
    [x] tbody - A wrapper for the rows of a table or informal table
    [x] td - A table entry in an HTML table
    [x] term - The word or phrase being defined or described in a variable list
    [ ] termdef - An inline term definition
    [ ] tertiary - A tertiary word or phrase in an index term
    [ ] tertiaryie - A tertiary term in an index entry, rather than in the text
    [ ] textdata - Pointer to external text data
    [ ] textobject - A wrapper for a text description of an object and its
        associated meta-information
    [ ] tfoot - A table footer consisting of one or more rows
    [x] tgroup - A wrapper for the main content of a table, or part of a table
    [x] th - A table header entry in an HTML table
    [x] thead - A table header consisting of one or more rows
    [x] tip - A suggestion to the user, set off from the text
    [x] title - The text of the title of a section of a document or of a formal
        block-level element
    [x] titleabbrev - The abbreviation of a Title
    [x] toc - A table of contents
    [x] tocback - An entry in a table of contents for a back matter component
    [x] tocchap - An entry in a table of contents for a component in the body of
        a document
    [x] tocentry - A component title in a table of contents
    [x] tocfront - An entry in a table of contents for a front matter component
    [x] toclevel1 - A top-level entry within a table of contents entry for a
        chapter-like component
    [x] toclevel2 - A second-level entry within a table of contents entry for a
        chapter-like component
    [x] toclevel3 - A third-level entry within a table of contents entry for a
        chapter-like component
    [x] toclevel4 - A fourth-level entry within a table of contents entry for a
        chapter-like component
    [x] toclevel5 - A fifth-level entry within a table of contents entry for a
        chapter-like component
    [x] tocpart - An entry in a table of contents for a part of a book
    [ ] token - A unit of information
    [x] tr - A row in an HTML table
    [ ] trademark - A trademark
    [x] type - The classification of a value
    [x] ulink - A link that addresses its target by means of a URL
        (Uniform Resource Locator)
    [x] uri - A Uniform Resource Identifier
    [x] userinput - Data entered by the user
    [x] varargs - An empty element in a function synopsis indicating a variable
        number of arguments
    [x] variablelist - A list in which each entry is composed of a set of one or
        more terms and an associated description
    [x] varlistentry - A wrapper for a set of terms and the associated description
        in a variable list
    [x] varname - The name of a variable
    [ ] videodata - Pointer to external video data
    [ ] videoobject - A wrapper for video data and its associated meta-information
    [ ] void - An empty element in a function synopsis indicating that the
        function in question takes no arguments
    [ ] volumenum - The volume number of a document in a set (as of books in a set
        or articles in a journal)
    [x] warning - An admonition set off from the text
    [x] wordasword - A word meant specifically as a word and not representing
        anything else
    [x] xref - A cross reference to another part of the document
    [ ] year - The year of publication of a document
    [x] ?asciidoc-br? - line break from asciidoc docbook output
    -}

    type DB = ExceptT PandocError (State DBState)

    data DBState = DBState{ dbSectionLevel :: Int
                          , dbQuoteType    :: QuoteType
                          , dbMeta         :: Meta
                          , dbAcceptsMeta  :: Bool
                          , dbBook         :: Bool
                          , dbFigureTitle  :: Inlines
                          , dbContent      :: [Content]
                          } deriving Show

    instance Default DBState where
      def = DBState{ dbSectionLevel = 0
                   , dbQuoteType = DoubleQuote
                   , dbMeta = mempty
                   , dbAcceptsMeta = False
                   , dbBook = False
                   , dbFigureTitle = mempty
                   , dbContent = [] }

    readDocBook :: ReaderOptions -> String -> Either PandocError Pandoc
    readDocBook _ inp  = (\blocks -> Pandoc (dbMeta st') (toList . mconcat $ blocks)) <$>  bs
      where (bs , st') = flip runState (def{ dbContent = tree }) . runExceptT . mapM parseBlock $ tree
            tree = normalizeTree . parseXML . handleInstructions $ inp

    -- We treat <?asciidoc-br?> specially (issue #1236), converting it
    -- to <br/>, since xml-light doesn't parse the instruction correctly.
    -- Other xml instructions are simply removed from the input stream.
    handleInstructions :: String -> String
    handleInstructions ('<':'?':'a':'s':'c':'i':'i':'d':'o':'c':'-':'b':'r':'?':'>':xs) = '<':'b':'r':'/':'>': handleInstructions xs
    handleInstructions xs = case break (=='<') xs of
                                 (ys, [])     -> ys
                                 ([], '<':zs) -> '<' : handleInstructions zs
                                 (ys, zs) -> ys ++ handleInstructions zs

    getFigure :: Element -> DB Blocks
    getFigure e = do
      tit <- case filterChild (named "title") e of
                  Just t -> getInlines t
                  Nothing -> return mempty
      modify $ \st -> st{ dbFigureTitle = tit }
      res <- getBlocks e
      modify $ \st -> st{ dbFigureTitle = mempty }
      return res

    -- normalize input, consolidating adjacent Text and CRef elements
    normalizeTree :: [Content] -> [Content]
    normalizeTree = everywhere (mkT go)
      where go :: [Content] -> [Content]
            go (Text (CData CDataRaw _ _):xs) = xs
            go (Text (CData CDataText s1 z):Text (CData CDataText s2 _):xs) =
               Text (CData CDataText (s1 ++ s2) z):xs
            go (Text (CData CDataText s1 z):CRef r:xs) =
               Text (CData CDataText (s1 ++ convertEntity r) z):xs
            go (CRef r:Text (CData CDataText s1 z):xs) =
                 Text (CData CDataText (convertEntity r ++ s1) z):xs
            go (CRef r1:CRef r2:xs) =
                 Text (CData CDataText (convertEntity r1 ++ convertEntity r2) Nothing):xs
            go xs = xs

    convertEntity :: String -> String
    convertEntity e = maybe (map toUpper e) (:[]) (lookupEntity e)

    -- convenience function to get an attribute value, defaulting to ""
    attrValue :: String -> Element -> String
    attrValue attr elt =
      case lookupAttrBy (\x -> qName x == attr) (elAttribs elt) of
        Just z  -> z
        Nothing -> ""

    -- convenience function
    named :: String -> Element -> Bool
    named s e = qName (elName e) == s

    --

    acceptingMetadata :: DB a -> DB a
    acceptingMetadata p = do
      modify (\s -> s { dbAcceptsMeta = True } )
      res <- p
      modify (\s -> s { dbAcceptsMeta = False })
      return res

    checkInMeta :: Monoid a => DB () -> DB a
    checkInMeta p = do
      accepts <- dbAcceptsMeta <$> get
      when accepts p
      return mempty

    addMeta :: ToMetaValue a => String -> a -> DB ()
    addMeta field val = modify (setMeta field val)

    instance HasMeta DBState where
      setMeta field v s =  s {dbMeta = setMeta field v (dbMeta s)}
      deleteMeta field s = s {dbMeta = deleteMeta field (dbMeta s)}

    isBlockElement :: Content -> Bool
    isBlockElement (Elem e) = qName (elName e) `elem` blocktags
      where blocktags = ["toc","index","para","formalpara","simpara",
               "ackno","epigraph","blockquote","bibliography","bibliodiv",
               "biblioentry","glossee","glosseealso","glossary",
               "glossdiv","glosslist","chapter","appendix","preface",
               "bridgehead","sect1","sect2","sect3","sect4","sect5","section",
               "refsect1","refsect2","refsect3","refsection",
               "important","caution","note","tip","warning","qandadiv",
               "question","answer","abstract","itemizedlist","orderedlist",
               "variablelist","article","book","table","informaltable",
               "informalexample",
               "screen","programlisting","example","calloutlist"]
    isBlockElement _ = False

    -- Trim leading and trailing newline characters
    trimNl :: String -> String
    trimNl = reverse . go . reverse . go
      where go ('\n':xs) = xs
            go xs        = xs

    -- meld text into beginning of first paragraph of Blocks.
    -- assumes Blocks start with a Para; if not, does nothing.
    addToStart :: Inlines -> Blocks -> Blocks
    addToStart toadd bs =
      case toList bs of
        (Para xs : rest) -> para (toadd <> fromList xs) <> fromList rest
        _                -> bs

    -- function that is used by both mediaobject (in parseBlock)
    -- and inlinemediaobject (in parseInline)
    -- A DocBook mediaobject is a wrapper around a set of alternative presentations
    getMediaobject :: Element -> DB Inlines
    getMediaobject e = do
      (imageUrl, attr) <-
        case filterChild (named "imageobject") e of
          Nothing  -> return (mempty, nullAttr)
          Just z   -> case filterChild (named "imagedata") z of
                        Nothing -> return (mempty, nullAttr)
                        Just i  -> let atVal a = attrValue a i
                                       w = case atVal "width" of
                                             "" -> []
                                             d  -> [("width", d)]
                                       h = case atVal "depth" of
                                             "" -> []
                                             d  -> [("height", d)]
                                       atr = (atVal "id", words $ atVal "role", w ++ h)
                                   in  return (atVal "fileref", atr)
      let getCaption el = case filterChild (\x -> named "caption" x
                                                || named "textobject" x
                                                || named "alt" x) el of
                            Nothing -> return mempty
                            Just z  -> mconcat <$> (mapM parseInline $ elContent z)
      figTitle <- gets dbFigureTitle
      let (caption, title) = if isNull figTitle
                                then (getCaption e, "")
                                else (return figTitle, "fig:")
      liftM (imageWith attr imageUrl title) caption

    getBlocks :: Element -> DB Blocks
    getBlocks e =  mconcat <$> (mapM parseBlock $ elContent e)

    parseBlock :: Content -> DB Blocks
    parseBlock (Text (CData CDataRaw _ _)) = return mempty -- DOCTYPE
    parseBlock (Text (CData _ s _)) = if all isSpace s
                                         then return mempty
                                         else return $ plain $ trimInlines $ text s
    parseBlock (CRef x) = return $ plain $ str $ map toUpper x
    parseBlock (Elem e) =
      case qName (elName e) of
            "toc"   -> return mempty -- skip TOC, since in pandoc it's autogenerated
            "index" -> return mempty -- skip index, since page numbers meaningless
            "para"  -> parseMixed para (elContent e)
            "formalpara" -> do
               tit <- case filterChild (named "title") e of
                            Just t  -> (para . strong . (<> str ".")) <$>
                                         getInlines t
                            Nothing -> return mempty
               (tit <>) <$> parseMixed para (elContent e)
            "simpara"  -> parseMixed para (elContent e)
            "ackno"  -> parseMixed para (elContent e)
            "epigraph" -> parseBlockquote
            "blockquote" -> parseBlockquote
            "attribution" -> return mempty
            "titleabbrev" -> return mempty
            "authorinitials" -> return mempty
            "title" ->  checkInMeta getTitle
            "author" -> checkInMeta getAuthor
            "authorgroup" -> checkInMeta getAuthorGroup
            "releaseinfo" -> checkInMeta (getInlines e >>= addMeta "release")
            "date" -> checkInMeta getDate
            "bibliography" -> sect 0
            "bibliodiv" -> sect 1
            "biblioentry" -> parseMixed para (elContent e)
            "bibliomixed" -> parseMixed para (elContent e)
            "glosssee" -> para . (\ils -> text "See " <> ils <> str ".")
                             <$> getInlines e
            "glossseealso" -> para . (\ils -> text "See also " <> ils <> str ".")
                             <$> getInlines e
            "glossary" -> sect 0
            "glossdiv" -> definitionList <$>
                      mapM parseGlossEntry (filterChildren (named "glossentry") e)
            "glosslist" -> definitionList <$>
                      mapM parseGlossEntry (filterChildren (named "glossentry") e)
            "chapter" -> sect 0
            "appendix" -> sect 0
            "preface" -> sect 0
            "bridgehead" -> para . strong <$> getInlines e
            "sect1" -> sect 1
            "sect2" -> sect 2
            "sect3" -> sect 3
            "sect4" -> sect 4
            "sect5" -> sect 5
            "section" -> gets dbSectionLevel >>= sect . (+1)
            "refsect1" -> sect 1
            "refsect2" -> sect 2
            "refsect3" -> sect 3
            "refsection" -> gets dbSectionLevel >>= sect . (+1)
            "important" -> blockQuote . (para (strong $ str "Important") <>)
                            <$> getBlocks e
            "caution" -> blockQuote . (para (strong $ str "Caution") <>)
                            <$> getBlocks e
            "note" -> blockQuote . (para (strong $ str "Note") <>)
                            <$> getBlocks e
            "tip" -> blockQuote . (para (strong $ str "Tip") <>)
                            <$> getBlocks e
            "warning" -> blockQuote . (para (strong $ str "Warning") <>)
                            <$> getBlocks e
            "area" -> return mempty
            "areaset" -> return mempty
            "areaspec" -> return mempty
            "qandadiv" -> gets dbSectionLevel >>= sect . (+1)
            "question" -> addToStart (strong (str "Q:") <> str " ") <$> getBlocks e
            "answer" -> addToStart (strong (str "A:") <> str " ") <$> getBlocks e
            "abstract" -> blockQuote <$> getBlocks e
            "calloutlist" -> bulletList <$> callouts
            "itemizedlist" -> bulletList <$> listitems
            "orderedlist" -> do
              let listStyle = case attrValue "numeration" e of
                                   "arabic"     -> Decimal
                                   "loweralpha" -> LowerAlpha
                                   "upperalpha" -> UpperAlpha
                                   "lowerroman" -> LowerRoman
                                   "upperroman" -> UpperRoman
                                   _            -> Decimal
              let start = fromMaybe 1 $
                          (attrValue "override" <$> filterElement (named "listitem") e)
                           >>= safeRead
              orderedListWith (start,listStyle,DefaultDelim)
                <$> listitems
            "variablelist" -> definitionList <$> deflistitems
            "figure" -> getFigure e
            "mediaobject" -> para <$> getMediaobject e
            "caption" -> return mempty
            "info" -> metaBlock
            "articleinfo" -> metaBlock
            "sectioninfo" -> return mempty  -- keywords & other metadata
            "refsectioninfo" -> return mempty  -- keywords & other metadata
            "refsect1info" -> return mempty  -- keywords & other metadata
            "refsect2info" -> return mempty  -- keywords & other metadata
            "refsect3info" -> return mempty  -- keywords & other metadata
            "sect1info" -> return mempty  -- keywords & other metadata
            "sect2info" -> return mempty  -- keywords & other metadata
            "sect3info" -> return mempty  -- keywords & other metadata
            "sect4info" -> return mempty  -- keywords & other metadata
            "sect5info" -> return mempty  -- keywords & other metadata
            "chapterinfo" -> return mempty  -- keywords & other metadata
            "glossaryinfo" -> return mempty  -- keywords & other metadata
            "appendixinfo" -> return mempty  -- keywords & other metadata
            "bookinfo" -> metaBlock
            "article" -> modify (\st -> st{ dbBook = False }) >>
                               getBlocks e
            "book" -> modify (\st -> st{ dbBook = True }) >>  getBlocks e
            "table" -> parseTable
            "informaltable" -> parseTable
            "informalexample" -> divWith ("", ["informalexample"], []) <$>
                                 getBlocks e
            "literallayout" -> codeBlockWithLang
            "screen" -> codeBlockWithLang
            "programlisting" -> codeBlockWithLang
            "?xml"  -> return mempty
            _       -> getBlocks e
       where parseMixed container conts = do
               let (ils,rest) = break isBlockElement conts
               ils' <- (trimInlines . mconcat) <$> mapM parseInline ils
               let p = if ils' == mempty then mempty else container ils'
               case rest of
                     []     -> return p
                     (r:rs) -> do
                        b <- parseBlock r
                        x <- parseMixed container rs
                        return $ p <> b <> x
             codeBlockWithLang = do
               let classes' = case attrValue "language" e of
                                    ""   -> []
                                    x    -> [x]
               return $ codeBlockWith (attrValue "id" e, classes', [])
                      $ trimNl $ strContentRecursive e
             parseBlockquote = do
                attrib <- case filterChild (named "attribution") e of
                                 Nothing  -> return mempty
                                 Just z   -> (para . (str "— " <>) . mconcat)
                                             <$> (mapM parseInline $ elContent z)
                contents <- getBlocks e
                return $ blockQuote (contents <> attrib)
             listitems = mapM getBlocks $ filterChildren (named "listitem") e
             callouts = mapM getBlocks $ filterChildren (named "callout") e
             deflistitems = mapM parseVarListEntry $ filterChildren
                         (named "varlistentry") e
             parseVarListEntry e' = do
                         let terms = filterChildren (named "term") e'
                         let items = filterChildren (named "listitem") e'
                         terms' <- mapM getInlines terms
                         items' <- mapM getBlocks items
                         return (mconcat $ intersperse (str "; ") terms', items')
             parseGlossEntry e' = do
                         let terms = filterChildren (named "glossterm") e'
                         let items = filterChildren (named "glossdef") e'
                         terms' <- mapM getInlines terms
                         items' <- mapM getBlocks items
                         return (mconcat $ intersperse (str "; ") terms', items')
             getTitle =  do
                         tit <- getInlines e
                         subtit <-  case filterChild (named "subtitle") e of
                                      Just s  -> (text ": " <>) <$>
                                                  getInlines s
                                      Nothing -> return mempty
                         addMeta "title" (tit <> subtit)

             getAuthor = (:[]) <$> getInlines e >>= addMeta "author"
             getAuthorGroup = do
              let terms = filterChildren (named "author") e
              mapM getInlines terms >>= addMeta "author"
             getDate = getInlines e >>= addMeta "date"
             parseTable = do
                          let isCaption x = named "title" x || named "caption" x
                          caption <- case filterChild isCaption e of
                                           Just t  -> getInlines t
                                           Nothing -> return mempty
                          let e' = fromMaybe e $ filterChild (named "tgroup") e
                          let isColspec x = named "colspec" x || named "col" x
                          let colspecs = case filterChild (named "colgroup") e' of
                                               Just c -> filterChildren isColspec c
                                               _      -> filterChildren isColspec e'
                          let isRow x = named "row" x || named "tr" x
                          headrows <- case filterChild (named "thead") e' of
                                           Just h  -> case filterChild isRow h of
                                                           Just x  -> parseRow x
                                                           Nothing -> return []
                                           Nothing -> return []
                          bodyrows <- case filterChild (named "tbody") e' of
                                           Just b  -> mapM parseRow
                                                      $ filterChildren isRow b
                                           Nothing -> mapM parseRow
                                                      $ filterChildren isRow e'
                          let toAlignment c = case findAttr (unqual "align") c of
                                                    Just "left"   -> AlignLeft
                                                    Just "right"  -> AlignRight
                                                    Just "center" -> AlignCenter
                                                    _             -> AlignDefault
                          let toWidth c = case findAttr (unqual "colwidth") c of
                                                    Just w -> fromMaybe 0
                                                       $ safeRead $ '0': filter (\x ->
                                                         (x >= '0' && x <= '9')
                                                          || x == '.') w
                                                    Nothing -> 0 :: Double
                          let numrows = case bodyrows of
                                             []   -> 0
                                             xs   -> maximum $ map length xs
                          let aligns = case colspecs of
                                         []  -> replicate numrows AlignDefault
                                         cs  -> map toAlignment cs
                          let widths = case colspecs of
                                         []  -> replicate numrows 0
                                         cs  -> let ws = map toWidth cs
                                                    tot = sum ws
                                                in  if all (> 0) ws
                                                       then map (/ tot) ws
                                                       else replicate numrows 0
                          let headrows' = if null headrows
                                             then replicate numrows mempty
                                             else headrows
                          return $ table caption (zip aligns widths)
                                     headrows' bodyrows
             isEntry x  = named "entry" x || named "td" x || named "th" x
             parseRow = mapM (parseMixed plain . elContent) . filterChildren isEntry
             sect n = do isbook <- gets dbBook
                         let n' = if isbook || n == 0 then n + 1 else n
                         headerText <- case filterChild (named "title") e `mplus`
                                            (filterChild (named "info") e >>=
                                                filterChild (named "title")) of
                                          Just t -> getInlines t
                                          Nothing -> return mempty
                         modify $ \st -> st{ dbSectionLevel = n }
                         b <- getBlocks e
                         let ident = attrValue "id" e
                         modify $ \st -> st{ dbSectionLevel = n - 1 }
                         return $ headerWith (ident,[],[]) n' headerText <> b
             metaBlock = acceptingMetadata (getBlocks e) >> return mempty

    getInlines :: Element -> DB Inlines
    getInlines e' = (trimInlines . mconcat) <$> (mapM parseInline $ elContent e')

    strContentRecursive :: Element -> String
    strContentRecursive = strContent .
      (\e' -> e'{ elContent = map elementToStr $ elContent e' })

    elementToStr :: Content -> Content
    elementToStr (Elem e') = Text $ CData CDataText (strContentRecursive e') Nothing
    elementToStr x = x

    parseInline :: Content -> DB Inlines
    parseInline (Text (CData _ s _)) = return $ text s
    parseInline (CRef ref) =
      return $ maybe (text $ map toUpper ref) (text . (:[])) $ lookupEntity ref
    parseInline (Elem e) =
      case qName (elName e) of
            "equation" -> equation displayMath
            "informalequation" -> equation displayMath
            "inlineequation" -> equation math
            "subscript" -> subscript <$> innerInlines
            "superscript" -> superscript <$> innerInlines
            "inlinemediaobject" -> getMediaobject e
            "quote" -> do
                qt <- gets dbQuoteType
                let qt' = if qt == SingleQuote then DoubleQuote else SingleQuote
                modify $ \st -> st{ dbQuoteType = qt' }
                contents <- innerInlines
                modify $ \st -> st{ dbQuoteType = qt }
                return $ if qt == SingleQuote
                            then singleQuoted contents
                            else doubleQuoted contents
            "simplelist" -> simpleList
            "segmentedlist" -> segmentedList
            "classname" -> codeWithLang
            "code" -> codeWithLang
            "filename" -> codeWithLang
            "literal" -> codeWithLang
            "computeroutput" -> codeWithLang
            "prompt" -> codeWithLang
            "parameter" -> codeWithLang
            "option" -> codeWithLang
            "optional" -> do x <- getInlines e
                             return $ str "[" <> x <> str "]"
            "markup" -> codeWithLang
            "wordasword" -> emph <$> innerInlines
            "command" -> codeWithLang
            "varname" -> codeWithLang
            "function" -> codeWithLang
            "type"    -> codeWithLang
            "symbol"  -> codeWithLang
            "constant" -> codeWithLang
            "userinput" -> codeWithLang
            "varargs" -> return $ code "(...)"
            "keycap" -> return (str $ strContent e)
            "keycombo" -> keycombo <$> (mapM parseInline $ elContent e)
            "menuchoice" -> menuchoice <$> (mapM parseInline $
                                            filter isGuiMenu $ elContent e)
            "xref" -> do
                content <- dbContent <$> get
                let linkend = attrValue "linkend" e
                let title = case attrValue "endterm" e of
                                ""      -> maybe "???" xrefTitleByElem (findElementById linkend content)
                                endterm -> maybe "???" strContent (findElementById endterm content)
                return $ link ('#' : linkend) "" (singleton (Str title))
            "email" -> return $ link ("mailto:" ++ strContent e) ""
                              $ str $ strContent e
            "uri" -> return $ link (strContent e) "" $ str $ strContent e
            "ulink" -> link (attrValue "url" e) "" <$> innerInlines
            "link" -> do
                 ils <- innerInlines
                 let href = case findAttr (QName "href" (Just "http://www.w3.org/1999/xlink") Nothing) e of
                                   Just h -> h
                                   _      -> ('#' : attrValue "linkend" e)
                 let ils' = if ils == mempty then str href else ils
                 let attr = (attrValue "id" e, words $ attrValue "role" e, [])
                 return $ linkWith attr href "" ils'
            "foreignphrase" -> emph <$> innerInlines
            "emphasis" -> case attrValue "role" e of
                                 "bold"   -> strong <$> innerInlines
                                 "strong" -> strong <$> innerInlines
                                 "strikethrough" -> strikeout <$> innerInlines
                                 _        -> emph <$> innerInlines
            "footnote" -> (note . mconcat) <$> (mapM parseBlock $ elContent e)
            "title" -> return mempty
            "affiliation" -> return mempty
            -- Note: this isn't a real docbook tag; it's what we convert
            -- <?asciidor-br?> to in handleInstructions, above.  A kludge to
            -- work around xml-light's inability to parse an instruction.
            "br" -> return linebreak
            _          -> innerInlines
       where innerInlines = (trimInlines . mconcat) <$>
                              (mapM parseInline $ elContent e)
             equation constructor = return $ mconcat $
               map (constructor . writeTeX)
               $ rights
               $ map (readMathML . showElement . everywhere (mkT removePrefix))
               $ filterChildren (\x -> qName (elName x) == "math" &&
                                       qPrefix (elName x) == Just "mml") e
             removePrefix elname = elname { qPrefix = Nothing }
             codeWithLang = do
               let classes' = case attrValue "language" e of
                                   "" -> []
                                   l  -> [l]
               return $ codeWith (attrValue "id" e,classes',[]) $ strContentRecursive e
             simpleList = (mconcat . intersperse (str "," <> space)) <$> mapM getInlines
                             (filterChildren (named "member") e)
             segmentedList = do
               tit <- maybe (return mempty) getInlines $ filterChild (named "title") e
               segtits <- mapM getInlines $ filterChildren (named "segtitle") e
               segitems <- mapM (mapM getInlines . filterChildren (named "seg"))
                              $ filterChildren (named "seglistitem") e
               let toSeg = mconcat . zipWith (\x y -> strong (x <> str ":") <> space <>
                                      y <> linebreak) segtits
               let segs = mconcat $ map toSeg segitems
               let tit' = if tit == mempty
                             then mempty
                             else strong tit <> linebreak
               return $ linebreak <> tit' <> segs
             keycombo = spanWith ("",["keycombo"],[]) .
                        mconcat . intersperse (str "+")
             menuchoice = spanWith ("",["menuchoice"],[]) .
                        mconcat . intersperse (text " > ")
             isGuiMenu (Elem x) = named "guimenu" x || named "guisubmenu" x ||
                                  named "guimenuitem" x
             isGuiMenu _        = False

             findElementById idString content
                = asum [filterElement (\x -> attrValue "id" x == idString) el | Elem el <- content]

             -- Use the 'xreflabel' attribute for getting the title of a xref link;
             -- if there's no such attribute, employ some heuristics based on what
             -- docbook-xsl does.
             xrefTitleByElem el
                 | not (null xrefLabel) = xrefLabel
                 | otherwise            = case qName (elName el) of
                      "chapter"      -> descendantContent "title" el
                      "sect1"        -> descendantContent "title" el
                      "sect2"        -> descendantContent "title" el
                      "sect3"        -> descendantContent "title" el
                      "sect4"        -> descendantContent "title" el
                      "sect5"        -> descendantContent "title" el
                      "cmdsynopsis"  -> descendantContent "command" el
                      "funcsynopsis" -> descendantContent "function" el
                      _              -> qName (elName el) ++ "_title"
              where
                xrefLabel = attrValue "xreflabel" el
                descendantContent name = maybe "???" strContent
                                       . findElement (QName name Nothing Nothing)