If the technical question was in a "take-home exam", as it were, or you otherwise had access to the internet, I'd figure you could look things up at will; to be

If the technical question was in a "take-home exam", as it were, or you otherwise had access to the internet, I'd figure you could look things up at will; to be on the safe side, perhaps ask "mind if I use php.net?". It's only reasonable -- you'd have access to the documentation when working in the field, after all. Being a good programmer isn't about knowing absolutely everything about the tools you're using, that'd be impossible -- being able to look up things you don't know is a very important skill. If, in a face-to-face interview, I were faced with something I didn't know, I'd say something like "I can't remember quite how this bit works, but I'd look it up on php.net/developer.mozilla.org/api.jquery.com/[appropriate reference]. Do you mind if I use pseudocode for the sake of getting on with the rest of the problem?" -- thus showing honesty, humility, the ability to use the resources available to you, and expedience.