set-case-syntax

set-case-syntax is a compiled Lisp function in `case-table.el'.

(set-case-syntax C SYNTAX TABLE)

Make character C case-invariant with syntax SYNTAX.
This sets the entry for character C in TABLE, which is a string
that will be used as the downcase part of a case table.
It also modifies `standard-syntax-table'.
SYNTAX should be " ", "w", "." or "_".