XPath operator
Comparison = and !=
Comparison against a node-set is existential, which makes != mean something other than 'not ='.
When one side is a node-set, = is true if *any* node in it satisfies the comparison. That rule is reasonable on its own and produces a genuinely surprising consequence: a != b is not the same as not(a = b).
For a set containing 2, 1 and 1: @qty != '1' is true, because some node differs. not(@qty = '1') is false, because some node matches. Both statements are correct and they disagree.
- Syntax
object = object- Returns
- boolean
- Kind
- Operator
- 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.
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
- boolean() and not()Converts to true or false. A node-set is true when it is non-empty — which is why [not(x)] means 'has no x'.
- Predicates [ ]Filters a node-set. Order matters, and a numeric predicate is not the same as a positional one applied afterwards.
- number()Converts to a number, producing NaN rather than an error when it cannot — which is how bad data passes silently.
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