public function has( $key )
	{
		if( empty( $key ) )																		//  no Key given
			throw new InvalidArgumentException( 'Key must not be empty.' );						//  throw Exception
		if( isset( $this->pairs[$key] ) )														//  Key is set on its own
			return TRUE;
		else																					//  Key has not been found
		{
			$key		.= $this->divider;														//  prepare Prefix Key to seach for
			foreach( $this->pairs as $pairKey => $pairValue )									//  iterate all stores Pairs
			{
				if( $pairKey[0] !== $key[0] )													//  precheck for Performance
					continue;																	//  skip Pair
				if( strpos( $pairKey, $key ) === 0 )											//  Prefix Key is found
					return TRUE;
			}
		}
		return FALSE;
	}