Accessibility: fix aria-hidden without value

[timroes]

Summary: Don't use aria-hidden without a value, use aria-hidden="true"

Currently there are some uses of aria-hidden without a value across the source code, e.g. in global_nav_link.html.

I assume that these were meant to hide the appropriate element (i.e. aria-hidden="true").

According to specification aria-hidden is not a boolean attribute. It can have values of true/false/undefined, which according to the type mapping appendix, maps to a keyword and enumerated attribute in HTML. For those you cannot skip the value, when you want the value to be true.

So this issue is for replacing all the aria-hiddens with aria-hidden="true".

But Tim, aren't you just terribly nitpicking about standards? Unfortunately no. I've seen a11y issues here, that are actually related to validators not correctly seeing that those elements are hidden from the a11y tree. Also, not following the spec might lead us to pure browser arbitrariness whether or not those elements really get hidden from the a11y tree (and at least the Chrome Accessibility Dev Tools also reports it as broken). So I think we should stick to the standard there and only use aria-hidden="true" with a value.

[cjcenizal]

Great catch -- thank you for pointing this out!