<% Layout.parent %>
render the title of the parent layout

Sourcecode in Layout/macros.js:
1:   function parent_macro(param) {
2:      if (param.as == "editor") {
3:         this._parent.renderParentLayoutChooser(this, param.firstOption);
4:      } else if (this.parent)
5:         return this.parent.title;
6:      return;
7:   }