$user: the User object that was created. (Parameter added in 1.7)
$byEmail: true when account was created "by email" (added in 1.12)
+'ValidateNewUser': Before user account is created, check account settings
+$user: the User object to be created.
+$&error: Error message, if any, returned by failed validation
+
'AfterFinalPageOutput': At the end of OutputPage::output() but before final
ob_end_flush() which will send the buffered output to the client. This allows
for last-minute modification of the output within the buffer by using