This diagram illustrates a sample document tree.
The root node (HTML) is at the top. It has two children: HEAD and BODY. HEAD has one child: TITLE. BODY has three children: H1, P, and UL. The UL has 3 LI leaf nodes.
In outline form, one . indenting for each level, that gives:
HTML .HEAD ..TITLE .BODY ..H1 ..P ..UL ...LI ...LI ...LI