Variable: case-fold-search
case-fold-search is a customizable and buffer-local variable defined
in buffer.c.
Documentation
Non-nil if searches and matches should ignore case.
Probably introduced at or before Emacs version 18.
Source Code
// Defined in /usr/src/emacs/src/buffer.c
DEFVAR_LISP ("case-fold-search", Vcase_fold_search,
doc: /* Non-nil if searches and matches should ignore case. */);