Variable: tabify-regexp
tabify-regexp is a variable defined in tabify.el.gz.
Value
" [ ]+"
Documentation
Regexp matching whitespace that tabify should consider.
Usually this will be " [ \\t]+" to match a space followed by whitespace.
"^\\t* [ \\t]+" is also useful, for tabifying only initial whitespace.
Source Code
;; Defined in /usr/src/emacs/lisp/tabify.el.gz
(defvar tabify-regexp " [ \t]+"
"Regexp matching whitespace that tabify should consider.
Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
\"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")