For the first non-nested matching pair of a and b in str, return an object with those keys: start the index of the first match of end the index of the matching b pre the preamble, a and b not included body the match, a and b not included post the postscript, a and b not included If there's no match, undefined will be returned. If the str contains more a than b / there are unmatched pairs, the first match that was closed will be used. For example, {{a} will match ['{', 'a', ''] and {a}} will match ['', 'a', '}']

For the first non-nested matching pair of a and b in str, return an array with indexes: [ <a index>, <b index> ].