+(defvar auto-mode-interpreter-regexp
+ "#![ \t]?\\([^ \t\n]*\
+/bin/env[ \t]\\)?\\([^ \t\n]+\\)"
+ "Regular expression matching interpreters, for file mode determination.
+This regular expression is matched against the first line of a file
+to determine the file's mode in `set-auto-mode' when Emacs can't deduce
+a mode from the file's name. If it matches, the file is assumed to
+be interpreted by the interpreter matched by the second group of the
+regular expression. The mode is then determined as the mode associated
+with that interpreter in `interpreter-mode-alist'.")
+