[csswg-drafts] [css-fonts-3] Is the exclusion of calc() from @font-feature-values intentional?

MatsPalmgren has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-fonts-3] Is the exclusion of calc() from @font-feature-values intentional? ==
I was writing some code to improve support for `calc()` in gecko
and I happened to accidentally support it in `@font-feature-values`,
specifically the NUMBER in the grammar here:
https://drafts.csswg.org/css-fonts-3/#basic-syntax
The prose says that NUMBER "are limited to integer values 0 or greater".
With that grammar + prose, `calc()` isn't allowed.  If the spec instead used
`<integer>` in the grammar then `calc()` would be allowed per:
https://drafts.csswg.org/css-values/#calc-notation

This makes `feature_value_definition` in `@font-feature-values` 
different from `<feature-tag-value>` in `font-feature-settings`:
https://drafts.csswg.org/css-fonts-3/#feature-tag-value
which use `<integer>` and thus allows `calc()` expressions.

Is this difference intentional?
(If so, it might be worth adding a note, or include a `calc()` in the example
that lists syntax errors, to make that clear.)

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/1127 using your GitHub account