/**
* Add new element to group.
*
* @param \DeForm\Element\ElementInterface $element
* @return self
* @throw \InvalidArgumentException
*/
public function addElement(ElementInterface $element)
{
if (false === $element instanceof RadioElement) {
throw new \InvalidArgumentException('Only instance of RadioElement object can be added.');
}
if ($this->countElements() > 0 && $element->getName() !== $this->getName()) {
throw new \InvalidArgumentException('Attribute input[name] is invalid.');
}
$this->elements[] = $element;
return $this;
}
