protected function validateKey($key)
    {
        $reserved = ['type', 'id'];
        if (in_array(strtolower($key), $reserved)) {
            throw MetadataException::reservedFieldKey($key, $reserved);
        }
    }
protected function validateKey($key)
    {
        $reserved = ['type', 'id'];
        if (in_array(strtolower($key), $reserved)) {
            throw MetadataException::reservedFieldKey($key, $reserved);
        }
    }
protected function validateKey ( $ key ) { $ reserved = [ 'type' , 'id' ] ; if ( in_array ( strtolower ( $ key ) , $ reserved ) ) { throw MetadataException :: reservedFieldKey ( $ key , $ reserved ) ; } }
Validates that the field key is not reserved.

@param   string  $key
@throws  MetadataException
Validates that the field key is not reserved .