[whatwg] Allow alt attribute with the span element

[Michael A. Peters]

With images, the alt attribute can and should be used to give a 
description of an image for users who can not see the image.

With text, some glyphs are pictographs that have a meaning. For example, 
U+1F502 is a pictograph indicating single loop, but it is meaningless if 
you can not see it.

Even if screen readers can specify the codepoint and/or map the 
codepoint to a description (do they?) sometimes fonts define PUA 
codepoints for pictograph glyphs that are not official.

A span element with a title attribute does not always solve this 
problem, sometimes the glyph is in a button element that has a title 
attribute describing what the button will do rather than the what the 
current state is.

For example, a button may show a single loop indicating the media is 
currently in single loop mode but have a title attribute specifying that 
pressing it enables continuous loop mode.

If there was an alt attribute on a span inside the button, screen 
readers could treat the span with a pictograph the same way it would 
treat an image child of a button attribute and describe the current 
pictograph to the end user.

If there is already a solution to this issue, I apologize, I could not 
find one.

We (er, WhatWG / W3C) could just add alt to the global attribute list 
too, rather than just span. Or come up with a semantic pictograph 
element specifically for this (just like we have tt and code).

Thank you for opinions.