As of PHP 5 the error reporting constant
E_STRICT is available, with the value 2048. When enabled, messages will be issued to warn you about code usage which is deprecated or which may not be future-proof.
E_ALLdoes not include
E_STRICT, so it's not enabled by default. You must explicitly set the error reporting level to include
E_STRICTin order to see these messages.
See Predefined Constants for more information.