Descendantorself

Descendant-or-self refers to an XPath axis used in XML path expressions. It selects the current context node and all of its descendants in the document tree. This axis is part of XPath 1.0 and 2.0, and is commonly employed in XSLT, XQuery, and related technologies to navigate hierarchical data.

In an XPath expression, the axis is written as descendant-or-self::. The node test that follows determines which nodes on that axis are included. For example, descendant-or-self::node() selects every node from the current node downward, including the current node. Using descendant-or-self::* selects all element nodes on and beneath the current node. A concrete usage is book/descendant-or-self::* to retrieve the book element and all of its descendant elements.

Key distinctions include the contrast with the descendant axis, which starts from the children of the context node and excludes the context node itself, and the self axis, which selects only the context node. The descendant-or-self axis therefore combines both capabilities, enabling concise queries that must consider both the starting node and all nodes below it.

Common use cases include locating all relevant elements within a subtree, filtering results by type or name, and combining with predicates to narrow results. It is frequently used in template rules, document querying, and data extraction tasks that involve recursive tree structures.

Overall, descendant-or-self is a foundational tool in XPath for subtree traversal, providing a simple way to include both a node and its entire downward hierarchy in a single axis.