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.
   
Note:
E_ALLdoes not includeE_STRICT, so it's not enabled by default. You must explicitly set the error reporting level to includeE_STRICTin order to see these messages.
See Predefined Constants for more information.