Additional functions within math functions that are permitted to be parsed depending on
the context of parsing (e.g. Parsing inset allows use of anchor() within calc()).
Dictates whether percentages are allowed in the calculation that
is parsed using this context, and whether such percentages have a
known “percent hint” (the type that they will eventually resolve to).
https://drafts.csswg.org/css-values-4/#calc-context