TinyMCE instances should link to their form labels

[Jono M]

The TinyMCE text editor is accessible in most screen readers, but if it is part of a form, the associated label is not read out when focusing the editor. For example, on the Profile page the "About me" editor is not linked to its label, making it harder for screen reader users to find out what the editor does.

This may not be fixable, since TinyMCE uses an iframe for its editing component, but should at least be looked into.

Affects latest master

[Jono M (jonom)]

It might actually be possible to add an aria-label or aria-labelledby attribute to the TinyMCE iframe (see http://stackoverflow.com/questions/4258701/tinymce-accessibility-label-for), although I'm not sure how straightforward this would be