protected function assertElement($element)
	{
		if ( !is_a($element, $this->elementClass) ) {
			$message = 'Collection element must be of "%s" class, but element of "%s" class given';

			throw new ElementCollectionException(
				sprintf($message, $this->elementClass, get_class($element)),
				ElementCollectionException::TYPE_ELEMENT_CLASS_MISMATCH
			);
		}

		return $this->acceptElement($element);
	}