docs: function traverseIdentifierInPattern(options, rootPattern, referencer, callback) {
      // Call the callback at left hand identifier nodes, and Collect right hand nodes.
      var visitor = new PatternVisitor(options, rootPattern, callback);
      visitor.visit(rootPattern);
  
      // Process the right hand nodes recursively.
      if (referencer != null) {
          visitor.rightHandNodes.forEach(referencer.visit, referencer);
      }
  }