footnotes extension - pulldown-cmark guide

Run this with cargo test --features gen-tests suite::footnotes.

Parts of this test case are based on https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702. Other parts were based on trial-and-error with GitHub's issue comment preview.

This spec describes nearly identical parsing to GFM, but not identical rendering. The HTML outputting module may be extended with features such as backreferences, but these are not built into the parser, and are unrelated to the syntax in any case. Alternative footnote rendering styles can be found in /examples/footnote-rewrite.rs.

Lorem ipsum.[^a] [^missing]

[^a]: Cool.

<p>Lorem ipsum.<sup class="footnote-reference"><a href="#a">1</a></sup> [^missing]</p>
<div class="footnote-definition" id="a"><sup class="footnote-definition-label">1</sup>
<p>Cool.</p>
</div>

Footnotes can be used inside blockquotes:

> This is the song that never ends.\
> Yes it goes on and on my friends.[^lambchops]
>
> [^lambchops]: <https://www.youtube.com/watch?v=0U2zJOryHKQ>

<blockquote>
<p>This is the song that never ends.<br />
Yes it goes on and on my friends.<sup class="footnote-reference"><a href="#lambchops">1</a></sup></p>
<div class="footnote-definition" id="lambchops"><sup class="footnote-definition-label">1</sup>
<p><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">https://www.youtube.com/watch?v=0U2zJOryHKQ</a></p>
</div>
</blockquote>

Footnotes can be complex block structures, but their contents must be indented first!

Without four spaces of indentation, no nesting:

Songs that simply loop are a popular way to annoy people. [^examples]

[^examples]:
 * [The song that never ends](https://www.youtube.com/watch?v=0U2zJOryHKQ)
 * [I know a song that gets on everybody's nerves](https://www.youtube.com/watch?v=TehWI09qxls)
 * [Ninety-nine bottles of beer on the wall](https://www.youtube.com/watch?v=qVjCag8XoHQ)

<p>Songs that simply loop are a popular way to annoy people. <sup class="footnote-reference"><a href="#examples">1</a></sup></p>
<div class="footnote-definition" id="examples"><sup class="footnote-definition-label">1</sup></div>
<ul>
<li><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">The song that never ends</a></li>
<li><a href="https://www.youtube.com/watch?v=TehWI09qxls">I know a song that gets on everybody's nerves</a></li>
<li><a href="https://www.youtube.com/watch?v=qVjCag8XoHQ">Ninety-nine bottles of beer on the wall</a></li>
</ul>

Yes, nesting:

Songs that simply loop are a popular way to annoy people. [^examples]

[^examples]:
    * [The song that never ends](https://www.youtube.com/watch?v=0U2zJOryHKQ)
    * [I know a song that gets on everybody's nerves](https://www.youtube.com/watch?v=TehWI09qxls)
    * [Ninety-nine bottles of beer on the wall](https://www.youtube.com/watch?v=qVjCag8XoHQ)

<p>Songs that simply loop are a popular way to annoy people. <sup class="footnote-reference"><a href="#examples">1</a></sup></p>
<div class="footnote-definition" id="examples"><sup class="footnote-definition-label">1</sup>
<ul>
<li><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">The song that never ends</a></li>
<li><a href="https://www.youtube.com/watch?v=TehWI09qxls">I know a song that gets on everybody's nerves</a></li>
<li><a href="https://www.youtube.com/watch?v=qVjCag8XoHQ">Ninety-nine bottles of beer on the wall</a></li>
</ul>
</div>

How this works with indented code blocks, blockquotes:

[^not-code] [^code] [^quote] [^not-quote] [^indented-quote]

[^not-code]:         not code

[^code]:
        code

[^quote]: > quote

[^not-quote]:
 > external quote

[^indented-quote]:
    > indented quote

<p><sup class="footnote-reference"><a href="#not-code">1</a></sup> <sup class="footnote-reference"><a href="#code">2</a></sup> <sup class="footnote-reference"><a href="#quote">3</a></sup> <sup class="footnote-reference"><a href="#not-quote">4</a></sup> <sup class="footnote-reference"><a href="#indented-quote">5</a></sup></p>
<div class="footnote-definition" id="not-code"><sup class="footnote-definition-label">1</sup>
<p>not code</p>
</div>
<div class="footnote-definition" id="code"><sup class="footnote-definition-label">2</sup>
<pre><code>code
</code></pre>
</div>
<div class="footnote-definition" id="quote"><sup class="footnote-definition-label">3</sup>
<blockquote><p>quote</p></blockquote>
</div>
<div class="footnote-definition" id="not-quote"><sup class="footnote-definition-label">4</sup></div>
<blockquote><p>external quote</p></blockquote><div class="footnote-definition" id="indented-quote"><sup class="footnote-definition-label">5</sup>
<blockquote><p>indented quote</p></blockquote>
</div>

Line breaks in paragraphs, however, are okay. Note that GitHub comments have hard line breaks without escapes, while Gists don't. To see compatible rendering with the examples in this file, try the code in a GitHub Gist file with a .md extension.

[^ab] [^cd]

[^ab]: a
b

[^cd]: c\
d

<p><sup class="footnote-reference"><a href="#ab">1</a></sup> <sup class="footnote-reference"><a href="#cd">2</a></sup></p>
<div class="footnote-definition" id="ab"><sup class="footnote-definition-label">1</sup>
<p>a
b</p>
</div>
<div class="footnote-definition" id="cd"><sup class="footnote-definition-label">2</sup>
<p>c<br>
d</p>
</div>

Footnotes can even have multiple paragraphs. You need to indent, though.

[^lorem]: If heaven ever wishes to grant me a boon, it will be a total effacing of the results of a mere chance which fixed my eye on a certain stray piece of shelf-paper. It was nothing on which I would naturally have stumbled in the course of my daily round, for it was an old number of an Australian journal, the Sydney Bulletin for April 18, 1925. It had escaped even the cutting bureau which had at the time of its issuance been avidly collecting material for my uncle's research.

I had largely given over my inquiries into what Professor Angell called the "Cthulhu Cult", and was visiting a learned friend in Paterson, New Jersey; the curator of a local museum and a mineralogist of note. Examining one day the reserve specimens roughly set on the storage shelves in a rear room of the museum, my eye was caught by an odd picture in one of the old papers spread beneath the stones. It was the Sydney Bulletin I have mentioned, for my friend had wide affiliations in all conceivable foreign parts; and the picture was a half-tone cut of a hideous stone image almost identical with that which Legrasse had found in the swamp.

[^ipsum]: If heaven ever wishes to grant me a boon, it will be a total effacing of the results of a mere chance which fixed my eye on a certain stray piece of shelf-paper. It was nothing on which I would naturally have stumbled in the course of my daily round, for it was an old number of an Australian journal, the Sydney Bulletin for April 18, 1925. It had escaped even the cutting bureau which had at the time of its issuance been avidly collecting material for my uncle's research.

    I had largely given over my inquiries into what Professor Angell called the "Cthulhu Cult", and was visiting a learned friend in Paterson, New Jersey; the curator of a local museum and a mineralogist of note. Examining one day the reserve specimens roughly set on the storage shelves in a rear room of the museum, my eye was caught by an odd picture in one of the old papers spread beneath the stones. It was the Sydney Bulletin I have mentioned, for my friend had wide affiliations in all conceivable foreign parts; and the picture was a half-tone cut of a hideous stone image almost identical with that which Legrasse had found in the swamp.

<div class="footnote-definition" id="lorem"><sup class="footnote-definition-label">1</sup>
<p>If heaven ever wishes to grant me a boon, it will be a total effacing of the results of a mere chance which fixed my eye on a certain stray piece of shelf-paper. It was nothing on which I would naturally have stumbled in the course of my daily round, for it was an old number of an Australian journal, the Sydney Bulletin for April 18, 1925. It had escaped even the cutting bureau which had at the time of its issuance been avidly collecting material for my uncle's research.</p>
</div>
<p>I had largely given over my inquiries into what Professor Angell called the "Cthulhu Cult", and was visiting a learned friend in Paterson, New Jersey; the curator of a local museum and a mineralogist of note. Examining one day the reserve specimens roughly set on the storage shelves in a rear room of the museum, my eye was caught by an odd picture in one of the old papers spread beneath the stones. It was the Sydney Bulletin I have mentioned, for my friend had wide affiliations in all conceivable foreign parts; and the picture was a half-tone cut of a hideous stone image almost identical with that which Legrasse had found in the swamp.</p>
<div class="footnote-definition" id="ipsum"><sup class="footnote-definition-label">2</sup>
<p>If heaven ever wishes to grant me a boon, it will be a total effacing of the results of a mere chance which fixed my eye on a certain stray piece of shelf-paper. It was nothing on which I would naturally have stumbled in the course of my daily round, for it was an old number of an Australian journal, the Sydney Bulletin for April 18, 1925. It had escaped even the cutting bureau which had at the time of its issuance been avidly collecting material for my uncle's research.</p>
<p>I had largely given over my inquiries into what Professor Angell called the "Cthulhu Cult", and was visiting a learned friend in Paterson, New Jersey; the curator of a local museum and a mineralogist of note. Examining one day the reserve specimens roughly set on the storage shelves in a rear room of the museum, my eye was caught by an odd picture in one of the old papers spread beneath the stones. It was the Sydney Bulletin I have mentioned, for my friend had wide affiliations in all conceivable foreign parts; and the picture was a half-tone cut of a hideous stone image almost identical with that which Legrasse had found in the swamp.</p>
</div>

A footnote will end on a single line break if the following paragraph isn't indented. Note that this behavior changed in version 0.1.0, to become more like hoedown. See issue #21.

[^ipsum]: How much wood would a woodchuck chuck.

If a woodchuck could chuck wood.


# Forms of entertainment that aren't childish

<div class="footnote-definition" id="ipsum"><sup class="footnote-definition-label">1</sup>
<p>How much wood would a woodchuck chuck.</p>
</div>
<p>If a woodchuck could chuck wood.</p>
<h1>Forms of entertainment that aren't childish</h1>

If the following footnote is indented, however, then it'll be included, regardless of how many blank lines separate it from the footnote definition. See https://gist.github.com/notriddle/39ffd52799604bc2cf923fe21a1ea0a9.

Footnotes [^one] [^many].

[^one]:





    first paragraph inside footnote

[^many]: first paragraph inside footnote





    second paragraph still inside footnote

<p>Footnotes <sup class="footnote-reference"><a href="#one">1</a></sup> <sup class="footnote-reference"><a href="#many">2</a></sup>.</p>
<div class="footnote-definition" id="one"><sup class="footnote-definition-label">1</sup>
<p>first paragraph inside footnote</p>
</div>
<div class="footnote-definition" id="many"><sup class="footnote-definition-label">2</sup>
<p>first paragraph inside footnote</p>
<p>second paragraph still inside footnote</p>
</div>

A footnote will also break if it's inside another container.

> He's also really stupid. [^why]
>
> [^why]: Because your mamma!

As such, we can guarantee that the non-childish forms of entertainment are probably more entertaining to adults, since, having had a whole childhood doing the childish ones, the non-childish ones are merely the ones that haven't gotten boring yet.

<blockquote>
<p>He's also really stupid. <sup class="footnote-reference"><a href="#why">1</a></sup></p>
<div class="footnote-definition" id="why"><sup class="footnote-definition-label">1</sup>
<p>Because your mamma!</p>
</div>
</blockquote>
<p>As such, we can guarantee that the non-childish forms of entertainment are probably more entertaining to adults, since, having had a whole childhood doing the childish ones, the non-childish ones are merely the ones that haven't gotten boring yet.</p>

As a special exception, footnotes cannot be nested directly inside each other. If they are, they act like they're declared beside each other.

Nested footnotes are considered poor style. [^a] [^xkcd] [^indent1] [^indent2]

[^a]: This does not mean that footnotes cannot reference each other. [^b]

[^b]: This means that a footnote definition cannot be directly inside another footnote definition.
> This means that a footnote cannot be directly inside another footnote's body. [^e]
>
> [^e]: They can, however, be inside anything else.

[^xkcd]: [The other kind of nested footnote is, however, considered poor style.](https://xkcd.com/1208/)

[^indent1]: indent1

    [^indent2]: indent2

<p>Nested footnotes are considered poor style. <sup class="footnote-reference"><a href="#a">1</a></sup> <sup class="footnote-reference"><a href="#xkcd">2</a></sup> <sup class="footnote-reference"><a href="#indent1">3</a></sup> <sup class="footnote-reference"><a href="#indent2">4</a></sup></p>
<div class="footnote-definition" id="a"><sup class="footnote-definition-label">1</sup>
<p>This does not mean that footnotes cannot reference each other. <sup class="footnote-reference"><a href="#b">5</a></sup></p>
</div>
<div class="footnote-definition" id="b"><sup class="footnote-definition-label">5</sup>
<p>This means that a footnote definition cannot be directly inside another footnote definition.</p>
</div>
<blockquote>
<p>This means that a footnote cannot be directly inside another footnote's body. <sup class="footnote-reference"><a href="#e">6</a></sup></p>
<div class="footnote-definition" id="e"><sup class="footnote-definition-label">6</sup>
<p>They can, however, be inside anything else.</p>
</div>
</blockquote>
<div class="footnote-definition" id="xkcd"><sup class="footnote-definition-label">2</sup>
<p><a href="https://xkcd.com/1208/">The other kind of nested footnote is, however, considered poor style.</a></p>
</div>
<div class="footnote-definition" id="indent1"><sup class="footnote-definition-label">3</sup>
<p>indent1</p>
</div>
<div class="footnote-definition" id="indent2"><sup class="footnote-definition-label">4</sup>
<p>indent2</p>
</div>

[^foo] [^bar]

[^foo]: [^bar]: 1

<p><sup class="footnote-reference"><a href="#foo">1</a></sup> <sup class="footnote-reference"><a href="#bar">2</a></sup></p>
<div class="footnote-definition" id="foo"><sup class="footnote-definition-label">1</sup></div>
<div class="footnote-definition" id="bar"><sup class="footnote-definition-label">2</sup>
<p>1</p>
</div>

They do not need one line between each other.

[^Doh] Ray Me Fa So La Te Do! [^1]

[^Doh]: I know. Wrong Doe. And it won't render right.
[^1]: Common for people practicing music.

<p><sup class="footnote-reference"><a href="#Doh">1</a></sup> Ray Me Fa So La Te Do! <sup class="footnote-reference"><a href="#1">2</a></sup></p>
<div class="footnote-definition" id="Doh"><sup class="footnote-definition-label">1</sup>
<p>I know. Wrong Doe. And it won't render right.</p>
</div>
<div class="footnote-definition" id="1"><sup class="footnote-definition-label">2</sup>
<p>Common for people practicing music.</p>
</div>

ISSUE 413

Lorem ipsum.[^a]

An unordered list before the footnotes:
* Ipsum
* Lorem

[^a]: Cool.

<p>Lorem ipsum.<sup class="footnote-reference"><a href="#a">1</a></sup></p>
<p>An unordered list before the footnotes:</p>
<ul>
<li>Ipsum</li>
<li>Lorem</li>
</ul>
<div class="footnote-definition" id="a"><sup class="footnote-definition-label">1</sup>
<p>Cool.</p>
</div>

Test case for more footnotes with list. Note that, while the DOM produced here is similar to GitHub's DOM (except GitHub reorders all footnotes to the end), they have a weird flexbox setup that causes lists nested inside footnotes to look really weird.

https://gist.github.com/notriddle/07360ab169c650b72ab8921089b12456

Songs that simply loop are a popular way to annoy people. [^examples]

[^examples]: * [The song that never ends](https://www.youtube.com/watch?v=0U2zJOryHKQ)
* [I know a song that gets on everybody's nerves](https://www.youtube.com/watch?v=TehWI09qxls)
* [Ninety-nine bottles of beer on the wall](https://www.youtube.com/watch?v=qVjCag8XoHQ)


Songs that simply loop are a popular way to annoy people. [^examples2]

[^examples2]: * [The song that never ends](https://www.youtube.com/watch?v=0U2zJOryHKQ) 2
    * [I know a song that gets on everybody's nerves](https://www.youtube.com/watch?v=TehWI09qxls) 2
    - [Ninety-nine bottles of beer on the wall](https://www.youtube.com/watch?v=qVjCag8XoHQ) 2


Songs that simply loop are a popular way to annoy people. [^examples3]

[^examples3]: * [The song that never ends](https://www.youtube.com/watch?v=0U2zJOryHKQ) 3

    * [I know a song that gets on everybody's nerves](https://www.youtube.com/watch?v=TehWI09qxls) 3

    * [Ninety-nine bottles of beer on the wall](https://www.youtube.com/watch?v=qVjCag8XoHQ) 3

<p>Songs that simply loop are a popular way to annoy people. <sup class="footnote-reference"><a href="#examples">1</a></sup></p>
<div class="footnote-definition" id="examples"><sup class="footnote-definition-label">1</sup>
<ul>
<li><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">The song that never ends</a></li>
</ul>
</div>
<ul>
<li><a href="https://www.youtube.com/watch?v=TehWI09qxls">I know a song that gets on everybody's nerves</a></li>
<li><a href="https://www.youtube.com/watch?v=qVjCag8XoHQ">Ninety-nine bottles of beer on the wall</a></li>
</ul>
<p>Songs that simply loop are a popular way to annoy people. <sup class="footnote-reference"><a href="#examples2">2</a></sup></p>
<div class="footnote-definition" id="examples2"><sup class="footnote-definition-label">2</sup>
<ul>
<li><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">The song that never ends</a> 2</li>
<li><a href="https://www.youtube.com/watch?v=TehWI09qxls">I know a song that gets on everybody's nerves</a> 2</li>
</ul>
<ul>
<li><a href="https://www.youtube.com/watch?v=qVjCag8XoHQ">Ninety-nine bottles of beer on the wall</a> 2</li>
</ul>
</div>
<p>Songs that simply loop are a popular way to annoy people. <sup class="footnote-reference"><a href="#examples3">3</a></sup></p>
<div class="footnote-definition" id="examples3"><sup class="footnote-definition-label">3</sup>
<ul>
<li><p><a href="https://www.youtube.com/watch?v=0U2zJOryHKQ">The song that never ends</a> 3</p>
</li><li><p><a href="https://www.youtube.com/watch?v=TehWI09qxls">I know a song that gets on everybody's nerves</a> 3</p>
</li><li><p><a href="https://www.youtube.com/watch?v=qVjCag8XoHQ">Ninety-nine bottles of beer on the wall</a> 3</p></li>
</ul>
</div>

Test case for the relationship between link references and footnotes. https://gist.github.com/notriddle/5625a3c1cb70b3067a01d7465f9d10f1

GitHub writes My [cmark-gfm]<sup class="footnote-reference"><a href="#examples">1</a></sup>. in the first paragraph. This seems like a bug, and it's easier to fix it than to remain compatible with it https://github.com/pulldown-cmark/pulldown-cmark/pull/929.

My [cmark-gfm][^c].

My [cmark-gfm][cmark-gfm][^c].

My [cmark-gfm][][^c].

My [cmark-gfm] [^c].

My [cmark-gfm[^c]].

[cmark-gfm]: https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702

[^c]: cmark-gfm is under the MIT license, so incorporating parts of its
    test suite into pulldown-cmark should be fine.


My [otherlink[^c]].

[otherlink[^c]]: https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702

<p>My <a href="https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702">cmark-gfm</a><sup class="footnote-reference"><a href="#c">1</a></sup>.</p>
<p>My <a href="https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702">cmark-gfm</a><sup class="footnote-reference"><a href="#c">1</a></sup>.</p>
<p>My <a href="https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702">cmark-gfm</a><sup class="footnote-reference"><a href="#c">1</a></sup>.</p>
<p>My <a href="https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702">cmark-gfm</a> <sup class="footnote-reference"><a href="#c">1</a></sup>.</p>
<p>My [cmark-gfm<sup class="footnote-reference"><a href="#c">1</a></sup>].</p>
<div class="footnote-definition" id="c"><sup class="footnote-definition-label">1</sup>
<p>cmark-gfm is under the MIT license, so incorporating parts of its
test suite into pulldown-cmark should be fine.</p>
</div>
<p>My [otherlink<sup class="footnote-reference"><a href="#c">1</a></sup>].</p>
<p>[otherlink<sup class="footnote-reference"><a href="#c">1</a></sup>]: https://github.com/github/cmark-gfm/blob/1e230827a584ebc9938c3eadc5059c55ef3c9abf/test/extensions.txt#L702</p>

If a footnote definition is followed by text indented four spaces or one tab, that text will be treated as part of the footnote instead of being an indented code block. To preserve the current behavior, writing code that will be interpreted the same way under both editions, separate the code block from the footnote using an un-indented HTML comment:

[^1]: footnote definition text

<!-- -->

    // indented code block
    fn main() {
        println!("hello world!");
    }

<div class="footnote-definition" id="1"><sup class="footnote-definition-label">1</sup>
<p>footnote definition text</p>
</div>
<!-- -->
<pre><code>// indented code block
fn main() {
    println!("hello world!");
}
</code></pre>

Footnote definitions no longer need to be separated by blank lines. To preserve the current behavior, if you intentionally want to write a footnote reference followed by a colon at the start of a line, use a backslash escape:

[^1]: footnote definition text
[^1]\: this is a reference, rather than a definition

<div class="footnote-definition" id="1"><sup class="footnote-definition-label">1</sup>
<p>footnote definition text
<sup class="footnote-reference"><a href="#1">1</a></sup>: this is a reference, rather than a definition</p>
</div>

If a footnote definition is immediately followed by a list, block quote, or table, it needs to be indented by four spaces to be considered part of the footnote. To preserve the current behavior, writing code that will be interpreted the same way in either edition, you'll need to fall back to HTML syntax, since there's no easy way to write code that the new syntax will accept as part of the footnote without the old syntax considering it a code block.

When migrating to the new Edition, a table within a footnote can be written like this (under the old Edition, the table is treated as source code):

[^1]:

    | column1 | column2 |
    |---------|---------|
    | row1a   | row1b   |
    | row2a   | row2b   |

<div class="footnote-definition" id="1"><sup class="footnote-definition-label">1</sup><table>
<thead>
<tr><th>column1</th><th>column2</th></tr>
</thead>
<tbody>
<tr><td>row1a</td><td>row1b</td></tr>
<tr><td>row2a</td><td>row2b</td></tr>
</tbody>
</table>
</div>

While Markdown Guide claims that you can't put footnote definitions inside lists, block quotes, or tables. When I try it in GitHub, footnote definitions are parsed when nested within lists and blockquotes, but not tables. A footnote definition will interrupt a table if it's at the start of a line, or just not be parsed if the table has a pipe at the start of the line.

* First
  [^1]: test
* Second [^1] test


> first
> [^2]: test
> Second [^2] test


   First   | Second
-----------|----------
first      | second
[^3]: test | test [^3]


|    First   | Second    |
|------------|-----------|
| first      | second    |
| [^4]: test | test [^4] |

> [^5]: * test [^5]

<ul>
<li>First
<div class="footnote-definition" id="1"><sup class="footnote-definition-label">1</sup>
<p>test</p>
</div>
</li>
<li>Second <sup class="footnote-reference"><a href="#1">1</a></sup> test</li>
</ul>
<blockquote>
<p>first</p>
<div class="footnote-definition" id="2"><sup class="footnote-definition-label">2</sup>
<p>test
Second <sup class="footnote-reference"><a href="#2">2</a></sup> test</p>
</div>
</blockquote>
<table><thead><tr><th>First</th><th>Second</th></tr></thead><tbody>
<tr><td>first</td><td>second</td></tr>
</tbody></table>
<div class="footnote-definition" id="3"><sup class="footnote-definition-label">3</sup>
<p>test | test <sup class="footnote-reference"><a href="#3">3</a></sup></p>
</div>
<table><thead><tr><th>First</th><th>Second</th></tr></thead><tbody>
<tr><td>first</td><td>second</td></tr>
<tr><td>[^4]: test</td><td>test [^4]</td></tr>
</tbody></table>
<blockquote>
<div class="footnote-definition" id="5"><sup class="footnote-definition-label">4</sup>
<ul>
<li>test <sup class="footnote-reference"><a href="#5">4</a></sup></li>
</ul>
</div>
</blockquote>

Footnote labels cannot be empty.

Test [^] link

[^]: https://rust-lang.org

<p>Test <a href="https://rust-lang.org">^</a> link</p>

Footnote labels cannot contain line breaks, even where link labels can.

[^foo\
bar]: not a footnote definition

[baz\
quux]: https://rust-lang.org

[first
second]: https://rust-lang.org

[^third
fourth]: not a footnote definition

[baz\
quux]
[^foo\
bar]
[first
second]
[^third
fourth]

<p>[^foo<br>
bar]: not a footnote definition</p>
<p>[^third
fourth]: not a footnote definition</p>
<p><a href="https://rust-lang.org">baz<br>
quux</a>
[^foo<br>
bar]
<a href="https://rust-lang.org">first
second</a>
[^third
fourth]</p>

The above rules imply a few cases where something starts with ^, but actually parses as a link definition.

[^foo
]: https://rust-lang.org

[^foo
]

<p><a href="https://rust-lang.org">^foo
</a></p>

Footnote definitions can be indented up to three spaces. At four spaces, it becomes a code block.

footnote [^baz]
footnote [^quux]

    [^quux]: x

   [^baz]: x

<p>footnote <sup class="footnote-reference"><a href="#baz">1</a></sup>
footnote [^quux]</p>
<pre><code>[^quux]: x
</code></pre>
<div class="footnote-definition" id="baz"><sup class="footnote-definition-label">1</sup>
<p>x</p>
</div>

Multiple footnotes should be able without needing whitespace in between.

Lorem ipsum.[^a][^b]

[^a]: Foo
[^b]: Bar

<p>Lorem ipsum.<sup class="footnote-reference"><a href="#a">1</a></sup><sup class="footnote-reference"><a href="#b">2</a></sup></p>
<div class="footnote-definition" id="a"><sup class="footnote-definition-label">1</sup>
<p>Foo</p>
</div>
<div class="footnote-definition" id="b"><sup class="footnote-definition-label">2</sup>
<p>Bar</p>
</div>

This does work already:

Lorem ipsum.[^a] [^b]

[^a]: Foo
[^b]: Bar

<p>Lorem ipsum.<sup class="footnote-reference"><a href="#a">1</a></sup> <sup class="footnote-reference"><a href="#b">2</a></sup></p>
<div class="footnote-definition" id="a"><sup class="footnote-definition-label">1</sup>
<p>Foo</p>
</div>
<div class="footnote-definition" id="b"><sup class="footnote-definition-label">2</sup>
<p>Bar</p>
</div>