How does (?:\;jsessionid=[^\?#]*)? in a regular expression work?

Question

Suppose I have this text to match:

http://localhost:8080/start.jsp;jsessionid=9E4CDB636248C9610F57704E5E07F782?whatever=true&somethingelse=true

Using this regular expression:

^(.*?start\.jsp)(?:\;jsessionid=[^\?#]*)?(\?[^#]*)?(#.*)?$

The resulting groups are:

1. http://localhost:8080/start.jsp
2. ?whatever=true&somethingelse=true

A. Why isn't group number 2 this: ;jsessionid=9E4CDB636248C9610F57704E5E07F782?
What does this part ?:\ at the beginning of second group do?

B. And also, how can I create an expression to extract the same groups as for the example above, if my options are begin.jsp and start.jsp (not just start.jsp) before the jsessionid part?

Answer 1

1. (?: ) is syntax for a non-capturing group. As the name explains it doesn't capture its match.
2. put alternate matching non-capturing group: (.*?(?:start|begin)\.jsp)