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PHP XPath

Query a loaded DOMDocument with its companion class, DOMXPath. evaluate() returns a native PHP value (number, string, or boolean) when the XPath expression's result is not a node-set, and a DOMNodeList otherwise. query() always returns a DOMNodeList, even for an expression such as count(...) that yields a number – converting that DOMNodeList to a string (for example via echo) raises a fatal error.

DOMXPath

readonly DOMDocument $document;
__construct(DOMDocument $doc)
mixed evaluate(string $expression [, DOMNode $contextnode [, bool $registerNodeNS = true]])
DOMNodeList query(string $expression [, DOMNode $contextnode [, bool $registerNodeNS = true]])
bool registerNamespace(string $prefix, string $namespaceURI)
void registerPhpFunctions([mixed $restrict])

ch08-xpath-people.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!-- people.xml -->
<people>
   <person id="p3">
      <name>Eric Lee</name>
      <gender>m</gender>
      <age>35</age>
   </person>
   <person id="p4">
      <name>Serena</name>
      <gender>f</gender>
      <age>25</age>
   </person>
</people>

<!DOCTYPE html>
<html><head></head><body><?php

$doc = new DOMDocument();
$doc->load('people.xml');
$xpath = new DOMXPath($doc);
$query = 'count(/people/person/name)';
echo $xpath->evaluate($query);  //2
echo $xpath->query($query); // error

?></body></html>

2 Catchable fatal error: Object of class DOMNodeList could not be converted to string in C:\Program Files\Zend\Apache2\htdocs\xml\people2.php on line 9