# Footnotes

## Summary

The Footnotes extension adds syntax for defining footnotes in Markdown documents.

This extension is included in the standard Markdown library.

## Syntax

Python-Markdown’s Footnote syntax follows the generally accepted syntax of the Markdown community at large and almost exactly matches PHP Markdown Extra’s implementation of footnotes. The only differences involve a few subtleties in the output.

Example:

    Footnotes[^1] have a label[^@#$%] and the footnote's content.

    [^1]: This is a footnote content.
    [^@#$%]: A footnote on the label: "@#$%".

A footnote label must start with a caret `^` and may contain any inline text (including spaces) between a set of square brackets `[]`. Only the first caret has any special meaning.

A footnote content must start with the label followed by a colon and at least one space. The label used to define the content must exactly match the label used in the body (including capitalization and white space). The content would then follow the label either on the same line or on the next line. The content may contain multiple lines, paragraphs, code blocks, blockquotes and most any other markdown syntax. The additional lines must be indented one level (four spaces or one tab).

When working with multiple blocks, it may be helpful to start the content on a separate line from the label which defines the content. This way the entire block is indented consistently and any errors are more easily discernible by the author.

    [^1]:
        The first paragraph of the definition.

        Paragraph two of the definition.

        > A blockquote with
        > multiple lines.

            a code block

        A final paragraph.

## Usage

See Extensions for general extension usage. Use `footnotes` as the name of the extension.

See the Library Reference for information about configuring extensions.

The following options are provided to configure the output:

- `PLACE_MARKER`: A text string used to mark the position where the footnotes are rendered. Defaults to `///Footnotes Go Here///`.

  If the place marker text is not found in the document, the footnote definitions are placed at the end of the resulting HTML document.

- `UNIQUE_IDS`: Whether to avoid collisions across multiple calls to `reset()`. Defaults to `False`.

- `BACKLINK_TEXT`: The text string that links from the footnote definition back to the position in the document. Defaults to `&#8617;`.

- `SUPERSCRIPT_TEXT`: The text string that links from the position in the document to the footnote definition. Defaults to `{}`, i.e. only the footnote’s number.

- `BACKLINK_TITLE`: The text string for the `title` HTML attribute of the footnote definition link. The placeholder `{}` will be replaced by the footnote number. Defaults to `Jump back to footnote {} in the text`.

- `SEPARATOR`: The text string used to set the footnote separator. Defaults to `:`.

A trivial example:

    markdown.markdown(some_text, extensions=['footnotes'])

## Resetting Instance State

Footnote definitions are stored within the `markdown.Markdown` class instance between multiple runs of the class. This allows footnotes from all runs to be included in output, with links and references that are unique, even though the class has been called multiple times.

However, if needed, the definitions can be cleared between runs by calling `reset`.

For instance, the home page of a blog might include the content from multiple documents. By not calling `reset`, all of the footnotes will be rendered, and they will all have unique links and references.

On the other hand, individual blog post pages might need the content from only one document, and should have footnotes pertaining only to that page. By calling `reset` between runs, the footnote definitions from the first document will be cleared before the second document is rendered.

An example of calling `reset`:

    md = markdown.Markdown(extensions=['footnotes'])
    html1 = md.convert(text_with_footnote)
    md.reset()
    html2 = md.convert(text_without_footnote)