category-set-mnemonics

category-set-mnemonics is a built-in function in `C source code'.

(category-set-mnemonics CATEGORY-SET)

Return a string containing mnemonics of the categories in CATEGORY-SET.
CATEGORY-SET is a bool-vector, and the categories "in" it are those
that are indexes where t occurs in the bool-vector.
The return value is a string containing those same categories.