Variable: indent-tabs-mode
indent-tabs-mode is a customizable and buffer-local variable defined
in simple.el.gz.
Documentation
Indentation can insert tabs if this is non-nil.
Probably introduced at or before Emacs version 18.
Key Bindings
Source Code
;; Defined in /usr/src/emacs/lisp/simple.el.gz
(define-minor-mode indent-tabs-mode
"Toggle whether indentation can insert TAB characters."
:group 'indent)