(PECL gupnp >= 0.1.0)
gupnp_service_proxy_add_notify — Sets up callback for variable change notification
$proxy
   , string $value
   , int $type
   , mixed $callback
   [, mixed $arg
  ] )Sets up callback to be called whenever a change notification for variable is recieved.
proxyA service proxy identifier.
valueThe variable to add notification for.
typeThe type of the variable. Type can be one of the following values:
GUPNP_TYPE_BOOLEANGUPNP_TYPE_INTGUPNP_TYPE_LONGGUPNP_TYPE_DOUBLEGUPNP_TYPE_FLOATGUPNP_TYPE_STRINGcallback
       The callback to call when variable changes. Typically, callback function 
       takes on three parameters. The variable 
       parameter being the first, value parameter
       being the second, and the arg is third.
      
arg
       User data for callback. 
      
   Returns TRUE on success or FALSE on failure.