DocumentTraversal contains methods that create NodeIterators and TreeWalkers to traverse a node and its children in document order (depth first, pre-order traversal, which is equivalent to the order in which the start tags occur in the text representation of the document).

Filters are objects that know how to "filter out" nodes.

NodeIterators are used to step through a set of nodes, e.g.

TreeWalker objects are used to navigate a document tree or subtree using the view of the document defined by their whatToShow flags and filter (if any).