[whatwg] Alt attribute for <video> and <audio>

[Remco]

My search was indeed too quick. I stand corrected.

Captions/subtitles seem like a very good idea for accessibility, but
in addition to that I think that an alt attribute would still be
appropriate for browsers that can't display the media at all. The alt
is a replacement for an external element that cannot be displayed at
all for whatever reason. It replaces the element. That's why I would
suggest alt attributes for objects, embeds, frames, etc. too.

Remco