Move xmlns to constants class

Author: ioigoume

src/XML/Constants.php

@@ -16,6 +16,11 @@ class Constants
      */
     public const NS_XML = 'http://www.w3.org/XML/1998/namespace';
 
+    /**
+     * The namespace for XMLNS declarations.
+     */
+    public const NS_XMLNS = 'http://www.w3.org/2000/xmlns/';
+
     /**
      * The maximum amount of child nodes this library is willing to handle.
      * By specification, this limit is 150K, but that opens up for denial of service.

src/XPath/XPath.php

@@ -71,8 +71,6 @@ public static function getXPath(DOMNode $node): DOMXPath
      */
     private static function registerAncestorNamespaces(DOMXPath $xp, DOMNode $node): void
     {
-        $xmlnsNs = 'http://www.w3.org/2000/xmlns/';
-
         // Avoid re-binding while walking upwards.
         $registered = [
             'xml' => true,
@@ -87,7 +85,7 @@ private static function registerAncestorNamespaces(DOMXPath $xp, DOMNode $node):
         while ($current instanceof DOMElement) {
             if ($current->hasAttributes()) {
                 foreach ($current->attributes as $attr) {
-                    if ($attr->namespaceURI !== $xmlnsNs) {
+                    if ($attr->namespaceURI !== C_XML::NS_XMLNS) {
                         continue;
                     }
                     $prefix = $attr->localName; // e.g., 'slate' for xmlns:slate, 'xmlns' for default