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1 (in
which the text nodes have been omitted for clarity).
Figure 6.1: The DOM tree
Each object in the DOM tree is called a node. There are several types of nodes,
including element nodes and text nodes. At the top of the tree is a document node,
which contains an element node called the root node; this is always the html element
in HTML and XHTML documents, and it branches into two child element
nodes??”head and body??”which then branch into other children.
A child node is structurally subordinate to its parent node. In HTML terms, this
means that the child??™s tags are nested inside the tags of the parent. For example, we
can see in Figure 6.1 that the h1 element is a child node of the body element and
the body element is the parent node of the h1 element. A node can be called a
141 CSS Layout and Formatting
descendant node if it??™s a child, grandchild, and so on, of another node. A node can
be called an ancestor node if it??™s a parent, grandparent, and so on, of another node.


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