WordPress MU

There are well over 1,000 hooks in Adam Brown's database. What is the best way to find the one that you need?

For example, I want to intercept the register user call and append on extra text to the username. I'm seeing user_register, and that gives me the username and email address to access, but I'm having trouble sending it back along. So I'm thinking that there has to be another hook somewhere that I use to complete the user registration. But it's like looking for a needle in a haystack sometimes.

Any thoughts on this?

Have you tried looking in the codex?

Yes, and that seems similar. Gotta know what you're looking for. I'm poking around and googling.