PHP | DOMNode lookupPrefix() Function

The DOMNode::lookupPrefix() function is an inbuilt function in PHP which is used to get the namespace prefix of the node based on the namespace URI.
Syntax:

string DOMNode::lookupPrefix( string $namespaceURI )

Parameters: This function accepts a single parameter $namespaceURI which holds the namespace URI.
Return Value: This function returns the prefix of the namespace.
Below examples illustrate the DOMNode::lookupPrefix() function in PHP:
Example 1:

php

<?php

// Create a new DOMDocument instance
$document = new DOMDocument();

// Load the XML with no namespace
$document->loadXML("<?xml version=\"1.0\"?>
    <div >
        <h1> GeeksforGeeks </h1>
    </div>
");

// Get the prefix with namespace URI "my_namespace"
$prefix = $document->documentElement->
           lookupPrefix("my_nsamespace");
echo $prefix;
?>

Output:

// Empty string as there is no such namespace

Example 2:

php

<?php

// Create a new DOMDocument instance
$document = new DOMDocument();

// Load the XML with a namespace with prefix x
$document->loadXML("<?xml version=\"1.0\"?>
    <div xmlns:x=\"my_namespace\">
        <x:h1 x:style=\"color:red;\">
         GeeksforGeeks
        </x:h1>
    </div>
");

// Get the prefix with namespace URI "my_namespace"
$prefix = $document->documentElement->
          lookupPrefix('my_namespace');
echo $prefix;
?>

Output:

x

Reference: https://www.php.net/manual/en/domnode.lookupprefix.php