二级目录，就是子目录，继承在主站目录下的，相当于在网站的根目录下再建立一个文件夹存放网站。
例如有酒店希望把“招聘”作为主要的导航栏目，尽管招聘是一个大标题下的二级目录。
For example a hotel may want to make "employment" a main navigational item, though it's clearly a secondary page that should be under a larger heading.
这些二级TOC条目中的每一个在项目中都有对应的XML文件目录。
Each of these secondary TOC entries has a corresponding table of contents XML file in the project.
应用推荐