如果在建立和插入屬性時引入了新的命名空間，createAttributeNS() 的行為與 createElementNS() 不同。
(1) 位置：使用 createAttributeNS() 時，新的命名空間會在文件元素的層級宣告。相反地，createElementNS() 會在受影響元素本身的層級宣告新的命名空間。
(2) 時機：使用 createAttributeNS() 時，新的命名空間會在屬性建立後立即在文件中宣告，實際上並不需要插入屬性。 createElementNS() 在元素未插入前不會影響文件。
範例
<?php
$source = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<root><tag></tag></root>
XML;
/*
I. createAttributeNS:
* a new namespace shows up immediately, even without insertion of the attribute
* the new namespace is declared at the level of the document element
*/
$doc = new DOMDocument( '1.0' );
$doc->loadXML( $source );
// (1) We just create a "namespace'd" attribute without appending it to any element.
$attr_ns = $doc->createAttributeNS( '{namespace_uri_here}', 'example:attr' );
print $doc->saveXML() . "\n";
/*
Result: The namespace declaration appears, having been added to the document element. Output:
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:example="{namespace_uri_here}"><tag/></root>
*/
// (2) Next, we give the attribute a value and insert it.
$attr_ns->value = 'value';
$doc->getElementsByTagName( 'tag' )->item(0)->appendChild( $attr_ns );
print $doc->saveXML() . "\n";
/*
Result: The "namespace'd" attribute shows up as well. Output:
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:example="{namespace_uri_here}"><tag example:attr="value"/></root>
*/
/*
II. createElementNS:
* a new namespace shows up only when the element is inserted
* the new namespace is declared at the level of the inserted element
*/
$doc = new DOMDocument( '1.0' );
$doc->loadXML( $source );
// (1) We create a "namespace'd" element without inserting it into the document.
$elem_ns = $doc->createElementNS( '{namespace_uri_here}', 'example:newtag' );
print $doc->saveXML() . "\n";
/*
Result: The document remains unchanged. Output:
<?xml version="1.0" encoding="UTF-8"?>
<root><tag/></root>
*/
// (2) Next, we insert the new element.
$doc->getElementsByTagName( 'tag' )->item(0)->appendChild( $elem_ns );
print $doc->saveXML() . "\n";
/*
Result: The namespace declaration appears, and it is embedded in the element using it. Output:
<?xml version="1.0" encoding="UTF-8"?>
<root><tag><example:newtag xmlns:example="{namespace_uri_here}"/></tag></root>
*/
?>