Muting Errors

Hey all, I happened to catch on an ambiguous page describing one of the PHP functions that you can "mute" errors from functions by using the "at" (@) character immediately before the function name. (e.g.: @objConnection = @mysql_connect(...);) I can't find any documentation on the PHP website other than the one liner I read on it. I was hoping someone may be able to send more info on it. What signals an "error"...is it a certain type of return variable that the @ sign recognizes, or what? Also, is it possible to instantiate my own errors within a function such that the calling PHP code can use the @ sign when calling my function to detect an error from my function? Thank you!