[css-text] Decimal digit transforms

Unicode has a character property to record its numeric value. This is mostly used for script-specific decimal digits, but also for precomposed vulgar fractions and other numerals. The relevant character classes are Nd Decimal Number, Nl Letter Number and No Other Number.

Antenna House Formatter supports a custom property number-transform. It does not just change the digit glyph, but the whole number. Besides Japanese-specific kansuji keywords, it accordingly accepts <list-style-type> as a value (and <string>).

I would like to propose something simpler, i.e. two new keywords – to be bikeshedded – for the text-transform property:

• global-digits: Use the respective glyph of U+0030…9 (0…9) for any Nd character with an integer Numeric Value of 0, …, 9. Note that font-variant-numeric will have an effect on those.
• local-digits: The inverse transformation, using the default digits of the native script derived from the language as returned by :lang(). This should also convert digits from other scripts, not just the international “ASCII” ones.

The former could be done with #3132, but the latter couldn’t.

Vulgar fractions, roman numerals etc. would be unaffected by these transformations.

Start with the proposed text-transform keywords, the Unicode Nd ranges listed here, and the relationship to issue #3132. Done would require a resolved CSS Working Group design for global-digits and local-digits, including their language and numeric-value behavior.