Matching with regex groups
rematches takes a pattern and compares it with a string.
If the pattern does not match the string then
nil is returned to show the function returned a false value.
(re-matches #"pumpkin" "Halloween pumpkin")
If there is an exact match and there are no groups (parens) in the regex, then the matched string is returned.
(re-matches #"pumpkin" "pumpkin")
If the pattern matches but there are groups, a vector of matching strings is returned. The first element in the vector is the entire match. The remaining elements are the group matches.
(re-matches #"Halloween(.*)" "Halloween pumpkin")