Some tags, of course, will be designed to be nested within others, but nothing is explicitly required to declare a tag as nestable.
当然，有些标记设计成嵌套在其它标记内，但是却不需要任何东西 来将标记显式地声明成是可嵌套的。
2
Developers and graphic designers can lay out an application's user interface using drag-and-drop controls and special nestable grids to manage and display complex content.