Markdown footnotes?

I would definitely like them. Although they could be hacked on via font-work, it would definitely enhance usability.

Here's what I do¹ to simulate footnotes:

These lines are _going to_ intersect<sup>1</sup>!

...

--------

**Footnotes:**

1. See Euclid's 5<sup>th</sup> postulate.

It's not that hard to do, but it's still a pain and the results aren't ideal. There's no easy way to set up links from the footnote mark to the footnote text and back again. Also, the footnote text ought to be smaller than then text in the body, but adding <sub>...</sub> tends to break the numbered items and I don't bother to play with it usually. It also gets tricky when editing in a new footnote since you need to manually adjust the numbering of notes that come after. Compared to using advanced links, roll-your-own footnotes seems practically barbaric.²

PHP Markdown Extra has a really cool footnote syntax³ that I'd like to have available on Stack Exchange:

These lines are _going to_ intersect[^1]!

...

[^1]: See Euclid's 5<sup>th</sup> postulate.

Just writing that example makes me yearn for footnote support; even the Markdown code looks clean! The output is more professional looking than my manual footnote technique and includes all sorts of niceties like auto-numbering and inline footnote text.

_Footnotes:

_{1. All the time!}

_{2. So why not just use links or parentheticals instead of footnotes? Because we aspire to the sort of answers expected in academia where footnotes are de rigueur. Plus it looks like you know what you are talking about and therefore encourages upvoting.}

_{3. Suggested in the comments by Arjan.}

Maybe they're not really useful on SO, but there are lots of places on *.SE where they could come in handy (e.g. cstheory).

I would very, very much like footnotes as used in xkcd's What If.  Very helpful for adding references or explanatory notes which otherwise detract from the main flow of an answer:

I definitely want this.

I've been using <sup>\*</sup> and <sup>\*\*</sup> and so on in the text and a --- rule followed by <sub>\*</sub> at the end, and it sort of works, but:

• I want the footnotes to be smaller/less important-looking, but on many browsers, subscript text is too small, as Eugene Siedel's answer shows.
• This is clearly an abuse of <sub>'s semantic meaning.
• <sub> doesn't work in combination with some other kinds of formatting. Part of the reason I use asterisks instead of numbered footnotes is to remind myself that auto-numbered lists and <sub> don't work together.
• <sub> does work with embedded code, but it looks ugly on most browsers.^* And that definitely affects SO. I have brief bits of code in my footnotes all the time.
• It would be much nicer for the reader if the footnotes were hyperlinked. (I know, I shouldn't be writing answers so long that it really matters. But the time I would spend editing one of them down, I could write book-sized answers on three other interesting questions I've found. :)
• I frequently screw up the number of asterisks, which is one of the reasons I end up re-editing my answers too often and annoying other people.
• I still catch myself using the years-obsolete <super> instead of the HTML5 <sup> tag, although that's probably just a problem with me. But it's kind of annoying that it actually works on some browsers, so I don't always notice it…

_{* How does this look for you? In particular, does the embedded code cause the lines to be spaced for full-sized text, even though the embedded code, like the rest of the text, is not full-sized?}

As we near the four-year mark since this Question was first asked, has the development team made any progress yet?

Footnotes are still a pain! And not only because jumping back and forth between text and footnote does not work. It is quite simply a usability nightmare! Here is an example where <sub> was used as a work-around to make footnote text:

On a normal notebook screen, who can read the text circled in red without getting severe eyestrain? Not I.

While we wait for a footnoting feature to be introduced, how about enabling the <small> HTML attribute so that footnotes can be the exact same point size as the text in comments (small but still readable)?

Not sure why I failed to leave a note here when declining, but... Better late than never.

We (the community manager team) sent this to the dev team for consideration in August of 2013; it was rejected for the following reasons:

1. We want to avoid creating proprietary additions to Markdown
2. We do not have consensus that footnotes are something to be encouraged
3. A work-around exists (albeit an ugly one)

If more than one of these reasons is invalidated at some point, we may be able to reconsider this request.

I don't know ¹.

¹ I just use superscript on it ².
² Looks nice to me.

What about recognizing footnote URLs (meaning: Extend the link discovery mechanism to URI schema footnote together with a suitable encoding for footnotes. Maybe add link targets to the same answer.)? My dirty solution until that looks like this¹:

Text[<sup>1</sup>][1]

[1]: http://footnote?Yes,_it's_ugly!.

So eventually one would be able to use a link like footnote: text..., so the footnote text might look like

[1]: footnote: Just the footnote text...

Need footnotes in community wiki mode. You don't want to disrupt the flow of someone else's discussion unnecessarily.

I believe this is unnecessary

I use footnotes regularly.¹ However, if I recall correctly, Stack Exchange's goal is to avoid lengthy answers. Answers are expected to be long enough to be thorough, but not so long as to threaten the Help Center's book rule. Consequently, the hyperlinks between the footnote and its source would be a convenience, but hardly a necessity. IMO, if someone's written an answer (or a question) so long that hyperlinking from the footnote reference to the footnote and back makes sense, the author should ponder long and hard about whether or not to summarize the answer/question or to vote to close the question for violating the book rule.

_{¹ Granted, they're a bit more manual than something cleaner and slicker....}