Not quite. (?!pattern) is a special assertion that says the regex should only succeed if pattern would not match at that point (see perlre). So the regex has two parts: , (comma) and (?! ) (not followed by a space).

Note that (?! ) (or it's positive counterpart (?= )) do not consume any part of the string. So /a(?=0)\d{2}/ applied to "a012" will match just "a01".

Changing it to have a + doesn't affect anything, since if it has more than one space after the comma, it definitely has one space.