protected function getHtmlClasses()
	{
		$classes = '';

		if( ! empty($this->css_classes) )
		{
			// open attribute
			$classes.= " class=\"";
			foreach($this->css_classes as $class)
			{
				$classes.="{$class} ";
			}
			// close attribute
			$classes.= "\"";
		}

		return $classes;
	}