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# HeaderId

## Summary

The HeaderId extension automatically generates `id` attributes for the header elements (`h1`-`h6`) in the resulting HTML document.

This extension is included in the standard Markdown library.

Warning

This extension is Pending Deprecation. The Table of Contents Extension should be used instead, which offers most the features of this extension and more.

## Syntax

By default, all headers will automatically have unique `id` attributes generated based upon the text of the header (see below to turn this off). Note this example, in which all three headers would have the same `id`:

    #Header
    #Header
    #Header

Results in:

    <h1 id="header">Header</h1>
    <h1 id="header_1">Header</h1>
    <h1 id="header_2">Header</h1>

## Usage

See Extensions for general extension usage, specify `markdown.extensions.headerid` as the name of the extension.

See the Library Reference for information about configuring extensions.

The following options are provided to configure the output:

- `level`: Base level for headers.

  Default: `1`

  The `level` setting allows you to automatically adjust the header levels to fit within the hierarchy of your HTML templates. For example, suppose the markdown text for a page should not contain any headers higher than level 3 (`<h3>`). The following will accomplish that:

      >>>  text = '''
      ... #Some Header
      ... ## Next Level'''
      >>> from markdown.extensions.headerid import HeaderIdExtension
      >>> html = markdown.markdown(text, extensions=[HeaderIdExtension(level=3)])
      >>> print html
      <h3 id="some_header">Some Header</h3>
      <h4 id="next_level">Next Level</h4>'

- `forceid`: Force all headers to have an id.

  Default: `True`

  The `forceid` setting turns on or off the automatically generated ids for headers that do not have one explicitly defined (using the Attribute List extension).

      >>> text = '''
      ... # Some Header
      ... # Header with ID # { #foo }'''
      >>> html = markdown.markdown(text,
                                   extensions=['markdown.extensions.attr_list',
                                               HeaderIdExtension(forceid=False)])
      >>> print html
      <h1>Some Header</h1>
      <h1 id="foo">Header with ID</h1>

- `separator`: Word separator. Character which replaces white space in id.

  Default: `-`

- `slugify`: Callable to generate anchors.

  Default: `markdown.extensions.headerid.slugify`

  If you would like to use a different algorithm to define the ids, you can pass in a callable which takes two arguments:

  - `value`: The string to slugify.
  - `separator`: The Word Separator.

## Using with Meta-Data

The HeaderId extension also supports the Meta-Data extension. Please see the documentation for that extension for specifics. The supported meta-data keywords are:

- `header_level`
- `header_forceid`

When used, the meta-data will override the settings provided through the
`extension_configs` interface.

This document:

    header_level: 2
    header_forceid: Off

    # A Header

Will result in the following output:

    <h2>A Header</h2>

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