/* Must return a reference to the array so that other methods can add instances */
	function &refPropertyDescriptors() {
		if (empty($this->propertyDescriptors)) {
			$this->propertyDescriptors = array();
			$className = $this->getName();
			if (!class_exists($className))
				throw new PntReflectionError("Class $className does not exist");
			// print "<BR>initializing propertyDescriptors of $className";
			$anInstance = new $className(); //initializes propertyDescriptors
		}
		return $this->propertyDescriptors;
	}