Show user variables that match PATTERN.
PATTERN can be a word, a list of words (separated by spaces),
or a regexp (using some regexp special characters). If it is a word,
search for matches for that word as a substring. If it is a list of words,
search for matches for any two (or more) of those words.
With C-u prefix, or if `apropos-do-all' is non-nil, also show normal variables.