Regex validation question


I'm trying to create a regex expression to validate text input. The correct input should be a series of 7 characters -- the 3 initial characters should be alphabetical (capitalization does not matter) and 4 following characters numerical. Eg, XXX0000. Could someone help me with constructing the regex expression to validate the user's input?


I'd definitely recommend using an online regex tester to work out this sort of thing, such as I believe this should do what you're asking for: