completion-regexp-list

completion-regexp-list is a variable defined in `C source code'.
Its value is

nil

Documentation:
List of regexps that should restrict possible completions.
The basic completion functions only consider a completion acceptable
if it matches all regular expressions in this list, with
`case-fold-search' bound to the value of `completion-ignore-case'.
See Info node `(elisp)Basic Completion', for a description of these
functions.