meta-begin-defun-regexp

meta-begin-defun-regexp is a variable defined in `meta-mode.el'.
Its value is

"\\(begin\\(char\\|fig\\|logochar\\)\\|def\\|mode_def\\|primarydef\\|secondarydef\\|tertiarydef\\|vardef\\)"

Documentation:
Regexp matching beginning of defuns in Metafont or MetaPost mode.

You can customize this variable.