The biggest unwritten requirement is if you'd want to spend and interact 40+ hours a week with that person.
This is certainly an important point, and ties into one of the things that really turns me off potential hires: admitting limitations.
I can't tell you how many times I've asked a question like "I see you've listed X, Y and Z as languages you are an expert in, but I don't see anything explaining where you have experience in language Y -- where did you use Y and what did you do with it?" and gotten answers anywhere from "Well, I used it for this one assignment in school" to "Part of the code I worked on talked to the piece written in Y, though I didn't actually work on that myself" to "Oh really? That's not supposed to be there".
Personally, I give absolutely zero craps about the specific languages and whether the job they are being considered for uses them or not: my philosophy is that any reasonable developer can learn any language / toolset necessary. But I do care very deeply that the people I work with are honest. I'd rather someone admit they don't know something than muddle through and not make any progress.
So when someone misrepresents themselves during the interview, this tells me a lot about their character and what it would be like working with them, and someone that doesn't admit their limitations is not someone I enjoy working with.
Seriously, no one knows everything. No one expects everyone to know everything. It's okay to say "I don't know" in an interview. One of two things will happen: The interviewee will get the job anyway, and the company will know they'll either have to invest in training them in the things they don't know or not have them do those things; or the interviewee won't get the job because they aren't qualified and the employer can't train them.
By the way, I've had the opposite response once, from a very junior developer: "Well I did it in school, and then also used it for this personal project, but didn't really think it was relevant for my resume since I didn't get paid". That person got the job (and some resume tips).