[css-text] Grammar of text-align doesn't allow combining <string> with a keyword

[Loirooriol]

https://drafts.csswg.org/css-text-4/#character-alignment

A keyword value may be specified in conjunction with the <string> value

https://drafts.csswg.org/css-text-4/#example-6a3cc5d3

TD { text-align: "." center }

But this is not in the grammar: https://drafts.csswg.org/css-text-4/#text-align-property

start | end | left | right | center | <string> | justify | match-parent | justify-all