I thought that using '(.*?)' would match up to 'b'

Why would it do that when it can match zero times?

1. (a) matches 1 character at position 0.
2. (.*?) attempts to match . 0 times at position 1.
3. (.*?) matches 0 character at at position 1.
4. (?:b=(\w))? attempts to match b=(\w) 1 times at position 1.
5. b=(\w) fails to match at position 1.
6. (?:b=(\w))? attempts to match b=(\w) 0 times at position 1.
7. (?:b=(\w))? matches 0 characters at at position 1.
8. Successful match.