userbldg.p will take the current user (as defined in common.i) and see if they are allowed to work with that personnel. If so, then TRUE is returned.
The way this works is that if they have no user-personnel record for this personnel, but they have entries for any other personnel, they are not allowed into this personnel. If they have absolutely no user-personnel records or the have one for this personnel, they are allowed to work with this personnel.