If zero or more characters at the beginning of string match
this regular expression, return a corresponding
MatchObject instance. Return None if the string does not
match the pattern; note that this is different from a zero-length
The optional second parameter pos gives an index in the string
where the search is to start; it defaults to 0. The
"^" pattern character will not match at the index where the
search is to start.
The optional parameter endpos limits how far the string will
be searched; it will be as if the string is endpos characters
long, so only the characters from pos to endpos will be
searched for a match.