[imsc] Add note about accessibility of subscript and superscript (#621)

nigelmegitt has just created a new issue for https://github.com/w3c/imsc:

== Add note about accessibility of subscript and superscript ==
As discussed at https://github.com/w3c/a11y-tracking/issues/252#issuecomment-3334994063 add an informative note for implementers to be aware of the need to ensure that the presented superscript/subscript text is visible as such to assistive technology.

For example something like:

>For implementations that use the CSS vertical-align property when mapping tts:fontVariant into HTML, use of vertical-align alone is insufficient for assistive technology to identify that the glyphs concerned are superscript or subscript.

or:

>Presentation implementations should mark up their output such that assistive technology can identify that the glyphs concerned are superscript or subscript. For example, use of the CSS `vertical-align` property alone could be insufficient.


Please view or discuss this issue at https://github.com/w3c/imsc/issues/621 using your GitHub account


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Received on Thursday, 13 November 2025 02:11:50 UTC