They are validating the username against several validation rules. One of them is 'eeUserName', which must match the following regex: ^(?=.*[0-9@_./-])(?=.*[a-zA-Z])([a-zA-Z0-9@_./-]){6,74}$ See if you can make heads or tails of it. I can't.

I'm going to have a nightmare about that regex, I just know it.