public function addCallback( $type, $callback ) {
		if ( !isset( $this->callbacks[$type] ) ) {
			$this->callbacks[$type] = [];
		}
		$this->callbacks[$type][] = $callback;
	}
public function addCallback( $type, $callback ) {
		if ( !isset( $this->callbacks[$type] ) ) {
			$this->callbacks[$type] = [];
		}
		$this->callbacks[$type][] = $callback;
	}
public function addCallback ( $ type , $ callback ) { if ( ! isset ( $ this -> callbacks [ $ type ] ) ) { $ this -> callbacks [ $ type ] = [ ] ; } $ this -> callbacks [ $ type ] [ ] = $ callback ; }
Register a callback that will be called for each page or category visited during the
traversal.
@param int $type One of the 'CALLBACK_' constants of this class.
@param callable $callback A callable that takes two \Mediawiki\DataModel\Page parameters.
Register a callback that will be called for each page or category visited during the traversal .