The DOM is an application programming interface that is linked to HTML, XHTML, or XML documents and treats these similar to a tree where each node in the tree represents a part of the document.
In simple words, the DOM can be compared to a tree where there is a root node, intermediate nodes, and leaf nodes.
The root node has no parent; the intermediate nodes have a parent, one or more siblings, and one or more children. This is a very important concept and will help at the time of creating relative or customized XPaths, which we will see in a later part of the chapter.
Shown here is a sample DOM:
In the preceding diagram, there are three leaf nodes, two intermediate nodes, and one root node. All of this is contained in a document. The question that arises next is: how do we get to a particular node in this tree structure? This is where terms such as XPath and...