code: function(obj, strategy, visitor, context) {
        var results = [];
        if (obj == null) return results;
        strategy(obj, function(value, key, parent) {
          if (visitor.call(context, value, key, parent)) results.push(value);
        }, null, this._traversalStrategy);
        return results;
      }
docs: Recursively traverses `obj` and returns all the elements that pass a truth test. `strategy` is the traversal function to use, e.g. `preorder` or `postorder`.