Question : php5 classes and lazy loading

Hello, this is an easy question.. when doing a class and calling a sub class in a function in the main class, does the subclass only get loaded when the function is run or is sub class loaded when the script that has the function that calls the sub class is loaded?  

Ex:
in file ScriptDeploy.php
class ScriptDeploy{
        public function validate($id){
              //the goal is not to load this till it's needed.
              return sdVal::val_It($id);
       }
}

in file class.sdVal.php

/// this should only load when the validate function is called in the class of ScriptDeploy
class sdVal extends ScriptDeploy{
       public function  function val_It($id){
              // stuff it does..
        }
}


My goal is to lighten the load, and make the scripts run as fast as possible, with the lightest memory usage as possible.  I think the lazy load works this way but info is a little muddy on this...   Thank you for the help.. Cheers -Jeremy

Answer : php5 classes and lazy loading

I see Word sorry!
To disable this restriction in Word 2007, change the value of the FileOpenBlock subkey.

source:
http://support.microsoft.com/kb/922849/