I think it's delicious how nobody, absolutely nobody, wants _ to mean "emphasis," they want italics, and yet despite there being a markdown-to-HTML build step nobody has ever done what they were told they were supposed to do to circumvent the semantic issue and use <span class="italic"> instead of <em>.
It wouldn't even make sense for markdown if it were language-agnostic to output <em> when that's HTML-only.
I'm going to go to my grave repeating that <em> is just <i> version 2.
Ahem. Org mode user here. _ means underline :-)
Emphasis/italics is using /
Totally fair. At least in part, I blame the choice of <em> and <strong>: it's really not clear what the hierarchy between them is, so I just think of them as the online versions of italic and bold.
<mild> and <strong>, or <em> and <emem> (or <double-em>, or <very-em>) might have been clearer, but at this point we'll never know.
Edit: apparently <i> has been redefined to be "the idiomatic text element" rather than just italic - so perhaps it's a semantically appropriate choice here after all! https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...