[imsc] Superscript/subscript support (#583)

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

== Superscript/subscript support ==
IMSC currently does not support superscript/subscript text, which is desirable (if not essential) in some languages.

French, for example, uses superscript to [abbreviate ordinal numerals](https://www.academie-francaise.fr/abreviations-des-adjectifs-numeraux). The same is true in English, albeit perhaps less necessary, e.g., _1st_ might be as acceptable as _1<sup>st</sup>_.

![image](https://github.com/user-attachments/assets/5cf3bdfa-f132-4e4d-bafc-f1ab1f2adb9c)

Couple of observations:

* Unicode does not have superscripts characters for all ordinal numerals, e.g., "er", "re", etc.
* TTML2 does not support HTML `sup`/`sub` markup.
* TTML2 supports `tts:fontVariant="super"` which is mapped to CSS `font-variant-position`, but (a) few fonts have super variants and (b) subscripting/superscripting seems more of a semantic or layout issue than a font/glyph selection issue.

CEA 708 has the concept of superscript/subscript (offset pen attribute).

In fact it looks like `tts:fontVariant` was [introduced, at least in part, to match CEA 708 capabilities](https://www.w3.org/AudioVideo/TT/tracker/issues/233), although, as mentioned above, it is not clear that it is a perfect match (or at least the mapping to CSS is not ideal).

Please view or discuss this issue at https://github.com/w3c/imsc/issues/583 using your GitHub account


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Received on Wednesday, 28 August 2024 22:55:34 UTC