Heres the long and short of it: set_error_handler() wants a string as the name of the function that will handle errors. However, if you create a class and try to assign error handling to a function within the class, there is no way to reference that function.

For example

class ApplicationObject {
	var $error_List as array();
	
	function ApplicationObject() {
		set_error_handler('trapError');
	}
	
	function trapError($err_no, $err_str, $err_file, $err_line, $err_context) {
		echo "Trap error caught error ".$err_no;
	}
}

// *** Now create the object ***
$app = new ApplicationObject(); 
trigger_error ("Cannot divide by zero", E_USER_ERROR);

This doesn't work. Nor does changing set_error_handler('trapError') to set_error_handler('$this->trapError'). Removing the quotes just executes the function. Removing the assignment of error handling outside of the class like so:
$app = new ApplicationObject(); 
set_error_handler('$app->trapError');
trigger_error ("Cannot divide by zero", E_USER_ERROR);

Since the error handling function will need access to $error_List and I sure dont want to GLOBAL it, this kind of makes things difficult.