I know another PHP developer that is well-known in the PHP community in DC - he told me a story about how he was a guest interviewer for another company as a courtesy once. Out of all of the candidates he interviewed, only one gave him straightforward, honest answers to the hard questions he asked - the answer was the same each time, "I don't know, I would google it". That was the candidate he selected, and supposedly it worked out great for that company.

Do not lie during an interview - if you don't know something, be honest and mention that you would do your research to figure it out.