[css-display] make invisible content available to AT

[dauwhe]

There seem to be lots of hacky ways to make web content visually hidden but available to assistive technologies.

Would box-suppress: hide be a solution for that issue? I've seen little discussion on how it would impact the accessibility tree.

EPUB is struggling with the lack of support for MathML. One thought was to include MathML, but by default display an image equivalent. Reading systems that support MathML could display the MathML through a user agent stylesheet. AT would always need to be able to use the MathML.

[aaaxx]

I can't upvote this highly enough. It would be really useful for designers to have a standard way to visually hide content, be it box-suppress or some other property.

[fantasai]

This is covered in the Speech module's speak property: https://www.w3.org/TR/css-speech/#speaking-props-speak

Perhaps it would be helpful to move it into the Display module to generate more interest? Alternately I've suggested trimming down the Speech module to consist solely of speak and speak-as.

[fantasai]

Closing as a duplicate of #560.