public function nextkey() {
		if ( $this->keys === null ) {
			return $this->firstkey();
		}

		return empty( $this->keys ) ? false : array_shift( $this->keys );
	}
public function nextkey() {
		if ( $this->keys === null ) {
			return $this->firstkey();
		}

		return empty( $this->keys ) ? false : array_shift( $this->keys );
	}
Fetch next key

@return string