XPath axe
descendant:: and descendant-or-self::
Everything below a node, at any depth. // is shorthand for descendant-or-self, which is why //a//b can be expensive.
descendant:: selects all nodes below the context at any depth; descendant-or-self:: also includes the context itself. The familiar // is an abbreviation for /descendant-or-self::node()/, which is why it can appear mid-path as well as at the start.
It is the most convenient axis and the most expensive: each // walks the whole subtree. Where you know the structure, an explicit path is faster and more precise.
- Syntax
descendant::name — // is descendant-or-self::node()/- Returns
- node-set
- Kind
- Axe
- Version
- XPath 1.0 (libxml2)
Worked examples
Each result below is what the evaluator returned, asserted on every test run. An empty result means an empty node-set — which is an answer, not an error.
What catches people out
- // at the start of an expression is absolute — it means 'anywhere in the document', not 'anywhere below here'. Use .// for the relative form.
- //a//b walks the subtree twice. On large documents that is the difference between instant and not.
- descendant:: does not include attributes.
The sample documents
Every example on this page runs against this document. The sitemap one is namespaced on purpose — almost every real XML document is, and that changes which expressions match.
<?xml version="1.0" encoding="UTF-8"?>
<order id="A-1001" tier="gold">
<customer country="NO">Ada Lovelace</customer>
<lines>
<line sku="WIDGET-1" qty="2"><price>14.50</price></line>
<line sku="WIDGET-2" qty="1"><price>39.00</price></line>
<line sku="GIFT-WRAP" qty="1"><price>0.00</price></line>
</lines>
<note> Deliver after 09:00 </note>
</order>Related
- child:: axisImmediate children. The default axis, which is why it is almost never written out.
- ancestor:: and ancestor-or-self::Every node above the context, up to the root. Returned in reverse document order.
- self:: axisThe context node itself. Abbreviated as a dot, and used to test what the current node is.
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