I was tempted to turn the two MUST-s into SHOULD-s; ignoring those terms is untestable in my view

I don't understand the point of this one, to be honest:

MUST ignore terms that it does not recognize.

This looks like a relic of when we thought epub:type might influence assistive technologies. What is it going to do with terms it doesn't recognize and why do we care?

I'd just erase it.

It should be possible to write a test for the "must" you're adding in this PR, though. Since we know pop-up footnotes are implemented on at least a couple of RSes, make a test document that tries to make a meta tag a footnote and see if it works.

It's not a perfect example of the requirement's restriction, but we only have to prove it can be done, right?

It should be possible to write a test for the "must" you're adding in this PR, though. Since we know pop-up footnotes are implemented on at least a couple of RSes, make a test document that tries to make a meta tag a footnote and see if it works.

It's not a perfect example of the requirement's restriction, but we only have to prove it can be done, right?

Actually, I did not know about the footnotes being implemented...

Let us see if this sketch for a test would work, containing two content files, p1 and p2

• On p1 have a proper footnote and see if the system implements it in the first place
• On p2, have a footnote term added to, say, the <title> element and show that that footnote is ignored

Is this what you mean? Which RS does implement a footnote with epub:type, b.t.w.? I mean, how would I test to see if the test itself is o.k.?

I was tempted to turn the two MUST-s into SHOULD-s; ignoring those terms is untestable in my view

I don't understand the point of this one, to be honest:

MUST ignore terms that it does not recognize.

This looks like a relic of when we thought epub:type might influence assistive technologies. What is it going to do with terms it doesn't recognize and why do we care?

I'd just erase it.

Happy to do it :-)

Which RS does implement a footnote with epub:type, b.t.w.?

iBooks was the first to implement them. You can read how to define them here: https://help.apple.com/itc/booksassetguide/en.lproj/itccf8ecf5c8.html

Thorium also has the same.

And just on a quick search there are some others like Calibre, Moon+, and even Kindle. I expect there are more, too.

Which RS does implement a footnote with epub:type, b.t.w.?

iBooks was the first to implement them. You can read how to define them here: https://help.apple.com/itc/booksassetguide/en.lproj/itccf8ecf5c8.html

Thorium also has the same.

And just on a quick search there are some others like Calibre, Moon+, and even Kindle. I expect there are more, too.

Brilliant! I have created two tests:

1. Essentially implementing what is in that apple note with an aside element
2. The same but the epub:type="footnote" id="the_note" is put on the title element.

According to our spec, but also according to its earlier incarnations, the title element text should not appear in a footnote popup. Guess what? It does in both Thorium and Apple Books...

Is it o.k. to merge this PR? I will add the anchor to these two tests, too, it will save another PR.

It does in both Thorium and Apple Books...

At least it's testable. I thought for sure they'd both ignore such a case, but I guess they aren't paying attention to where the semantic is set.

Is it o.k. to merge this PR?

Looks fine to me now.