Brr.RegexpSourceRegExp objects and matching.
create ?flags s is the regexp object for s using flags if specified.
exec r s executes regular expression r on s at index last_index.
fold_matches r f s acc folds f over the non-overlapping matches of r in s starintg with acc.
replace r ~by s replaces the first match of r by by in s.
replace_all r ~by s replaces all non-overlapping matches of r by by in s.
search r s is the first index of s that matches r or -1 if there is no match.
split r s splits s on delimiters matched by r.
set_last_index r i sets the last_index in r to i.
source r is the source text of r.