code: function concatenate(node, index, parent) {
          if (
              parent &&
              (parent.type === 'ParagraphNode' || parent.type === 'RootNode') &&
              queue.indexOf(parent) === -1
          ) {
              queue.push(parent);
          }
      }
docs: Gather a parent if not already gathered.
  
  @param {NLCSTChildNode} node - Child.
  @param {number} index - Position of `node` in
  `parent`.
  @param {NLCSTParentNode} parent - Parent of `child`.