Underlining is presentational information. I realise that the HTML5 spec changes the meaning of
<u>but this is quite confusing, and causal writers would probably think that the text should appear underlined.
Fair enough. Another approach could be just to define a set of separate class and avoid the <u> tag entirely. Or we can just stay practical, and know that in the real world, most browser is unlikely to diverge from treating <u> as underlined text.
There is the language of w3, and the is the language of real world users. We should strive to keep to w3 as much as possible, but don’t forget our Ghetto roots and lets not be afraid to break away as needed.
Btw here’s another approach to underlining as covered in http://talk.commonmark.org/t/highlights-strikeout-underlines/
>>__ underlined text __<<