Footnotes may not be easily solved for equivalence across HTML and Markdown and still return to DITA. The data models (indeed the intent behind the designs) is all different.
Markdown has a close proxy to footnotes in its "reference links", but HTML has no architected equivalent--rather than providing for a semantic structure with footnote-like behavior, HTML5 has you inserting markup that supports the behavior, but you cannot easily decompose it back into the intent of a reference link when converting into DITA. One Markdown extension suggests adding a caret into the reference (i.e., [^1] to imply a proper footnote, meaning that extended content can be ascribed to it (see http://rephrase.net/box/word/footnotes/syntax/). But since HTML has no way to be similarly extended, we are limited to whatever processing and display semantic are available.
One user has proposed a footnote design for a future HTML5, but don't hold your breath. It would be a properly architected structure for deferred content, but good ideas take time to win hearts, if ever. This proposal article (see http://davidmacd.com/blog/html51-footnotes.html) actually explains the ePub solution well, and it is compelling to me for now--I'm inclined to make use of <aside> for any sort of deferable content in HDITA structures (perhaps for <note> as well, if you can accept that it is deferable (or at least can be floated outside of the normal galley flow).
Meanwhile, although the details/summary markup does provide an architected design that represents content that can be deferred from the main view, it is more truthfully a visibility toggle, not a reference to a block of text. This is soo close, but I understand perfectly why ePub eschews its use as a footnote. This markup would better serve the role of a FAQ in which the question is the <details> and the answer is the <summary> content, with expanding behavior in the display.
Try pasting this content into a small HTML file and drop it onto a browser to see how HTML5 summary/details works.
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<p>The details element in HTML5 works best as an interaction that toggles visibility on and off. Normally this is done with spans and divs and a tiny bit of _javascript_ for the interaction. Note how content pushes down as summary content is toggled into view:</p>
So although it is useful to see how summary/details works, I consider it to be a UI gadget rather than a useful container for content. The nested containers are good, but their behavior precludes the intent of a footnote, in my opinion. I'd save this markup for FAQs and for progressive disclosure use cases.
<details>
<summary>Q: Why are markup architectures so difficult?</summary>
<p>A: Humans design solutions for different reasons.</p>
</details>
<details>
<summary>Q: Why do we care about what we do?</summary>
<p>A: Because we like to prevail over the limitations handed to us.</p>
</details>
<p>Note that this markup provides default behavior in the browser; no _javascript_ is needed. The downside is that the default presentation is ugly and not all browsers provide CSS hooks for styling yet.</p>
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I say let's see why the ePub solution is not better, and whether we can shoehorn <aside> as footnote into Markdown semantics like the reference link. I think this comes closest to lining up with DITA fn intent (especially with the caret extension).
I could be convinced that it is a useful design point to allow Lightweight DITA to be only as rich as there exist fully equivalent markup solutions across all versions (and common Markdown at that--extensions become liabilities outside the few environments that support them). 1 Designating and maintaining the record copy out of 3 near equivalents is a recipe for Version Control Induced Insanity.
--
Don
1 Of course, there is always "DITA used lightly" that I get a lot of present use out of. ;-)
On 4/18/2016 10:52 AM, Michael Priestley wrote:
Interesting discussion here, on how it's being done in EPUB and why:
http://idpf.org/forum/topic-885
Michael Priestley, Senior Technical Staff Member (STSM)
Enterprise Content Technology Strategist
mpriestl@ca.ibm.com
http://dita.xml.org/blog/michael-priestley
--
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