/**
* Get a specific field from a header like content type or all fields as array
*
* If the header occurs more than once, only the value from the first header
* is returned.
*
* Throws an Exception if the requested header does not exist. If
* the specific header field does not exist, returns null.
*
* @param string $name name of header, like in getHeader()
* @param string $wantedPart the wanted part, default is first, if null an array with all parts is returned
* @param string $firstName key name for the first part
* @return string|array wanted part or all parts as array($firstName => firstPart, partname => value)
* @throws \Zend\Mime\Exception\RuntimeException
*/
public function getHeaderField($name, $wantedPart = '0', $firstName = '0')
{
return Mime\Decode::splitHeaderField(current($this->getHeader($name, 'array')), $wantedPart, $firstName);
}