7.2 Headings and sections

7.2.1 Extension: auto_identifiers

A heading without an explicitly specified identifier will be automatically assigned a unique identifier based on the heading text.

This extension can be enabled/disabled for the following formats:

input formats

markdown, latex, rst, mediawiki, textile

output formats

markdown, muse

enabled by default in

markdown, muse

The default algorithm used to derive the identifier from the heading text is:

• Remove all formatting, links, etc.
• Remove all footnotes.
• Remove all non-alphanumeric characters, except underscores, hyphens, and periods.
• Replace all spaces and newlines with hyphens.
• Convert all alphabetic characters to lowercase.
• Remove everything up to the first letter (identifiers may not begin with a number or punctuation mark).
• If nothing is left after this, use the identifier section.

Thus, for example,

These rules should, in most cases, allow one to determine the identifier from the heading text. The exception is when several headings have the same text; in this case, the first will get an identifier as described above; the second will get the same identifier with -1 appended; the third with -2; and so on.

(However, a different algorithm is used if gfm_auto_identifiers is enabled; see below.)

These identifiers are used to provide link targets in the table of contents generated by the --toc|--table-of-contents option. They also make it easy to provide links from one section of a document to another. A link to this section, for example, might look like this:

See the section on
[heading identifiers](#heading-identifiers-in-html-latex-and-context).

Note, however, that this method of providing links to sections works only in HTML, LaTeX, and ConTeXt formats.

If the --section-divs option is specified, then each section will be wrapped in a section (or a div, if html4 was specified), and the identifier will be attached to the enclosing <section> (or <div>) tag rather than the heading itself. This allows entire sections to be manipulated using JavaScript or treated differently in CSS.

7.2.2 Extension: ascii_identifiers

Causes the identifiers produced by auto_identifiers to be pure ASCII. Accents are stripped off of accented Latin letters, and non-Latin letters are omitted.

7.2.3 Extension: gfm_auto_identifiers

Changes the algorithm used by auto_identifiers to conform to GitHub’s method. Spaces are converted to dashes (-), uppercase characters to lowercase characters, and punctuation characters other than - and _ are removed. Emojis are replaced by their names.