public function set( $selector, $key, $value = NULL ){
		if( $value === NULL || !strlen( $value ) )
			return $this->remove( $selector, $key );
		$rule = $this->getRuleBySelector( $selector );
		if( !$rule ){
			$rule	= new ADT_CSS_Rule( $selector );
			$this->rules[]	= $rule;
		}
		return $rule->setPropertyByKey( $key, $value );
	}