Namespace declaration attributes and prefixes are normalized as part of the normalizeDocument method of the Document interface as if the following method described in pseudo code was called on the document element.

void Element.normalizeNamespaces()
{

  // Pick up local namespace declarations
  // 
  for ( all DOM Level 2 valid local namespace declaration attributes of Element ) 
  {    
      if (the namespace declaration is invalid) 
      {
          // Note: The prefix xmlns is used only to declare namespace bindings and
          // is by definition bound to the namespace name http://www.w3.org/2000/xmlns/.
          // It must not be declared. No other prefix may be bound to this namespace name.         
               
          ==> Report an error.

      } 
      else 
      {
          ==>  Record the namespace declaration
      }
  }


  // Fixup element's namespace
  //
  if ( Element's namespaceURI != null )
  {
    if ( Element's prefix/namespace pair (or default namespace,
         if no prefix) are within the scope of a binding )
    {
      ==> do nothing, declaration in scope is inherited

      See section "B.1.1: Scope of a binding" for an example

    }
    else
    {
      ==> Create a local namespace declaration attr for this namespace,
          with Element's current prefix (or a default namespace, if
          no prefix). If there's a conflicting local declaration
          already present, change its value to use this namespace.

          See section "B.1.2: Conflicting namespace declaration" for an example

          // NOTE that this may break other nodes within this Element's
          // subtree, if they're already using this prefix.
          // They will be repaired when we reach them.
    }
  }
  else
  {
    // Element has no namespace URI:
    if ( Element's localName is null )
    {
       // DOM Level 1 node
       ==> if in process of validation against a namespace aware schema 
           (i.e XML Schema) report a fatal error: the processor can not recover 
           in this situation. 
           Otherwise, report an error: no namespace fixup will be performed on this node.
    }
    else
    {
      // Element has no pseudo-prefix
      if ( there's a conflicting local default namespace declaration
           already present )
      {
        ==> change its value to use this empty namespace.

      }
      // NOTE that this may break other nodes within this Element's
      // subtree, if they're already using the default namespaces.
      // They will be repaired when we reach them.
    }
  }


  // Examine and polish the attributes
  //
  for ( all non-namespace Attrs of Element )
  {
     if ( Attr[i] has a namespace URI )
     {
        if ( attribute has no prefix (default namespace decl does not apply to attributes) 
             OR
             attribute prefix is not declared
             OR
             conflict: attribute has a prefix that conflicts with a binding
                       already active in scope)
        {              
           if (namespaceURI matches an in scope declaration of one or more prefixes) 
           {
               // pick the most local binding available; 
               // if there is more than one pick one arbitrarily

               ==> change attribute's prefix.
           }
           else 
           {
               if (the current prefix is not null and it has no in scope declaration) 
               {
                   ==> declare this prefix
               } 
               else 
               {
                   // find a prefix following the pattern "NS" +index (starting at 1)
                   // make sure this prefix is not declared in the current scope.
                   // create a local namespace declaration attribute

                   ==> change attribute's prefix.
               }
           }           
        }
     }    
     else
     {
        // Attr[i] has no namespace URI
            
        if ( Attr[i] has no localName )
        {
           // DOM Level 1 node
           ==> if in process of validation against a namespace aware schema 
               (i.e XML Schema) report a fatal error: the processor can not recover 
                in this situation. 
                Otherwise, report an error: no namespace fixup will be performed on this node.
        }
        else
        { 
           // attr has no namespace URI and no prefix
           // no action is required, since attrs don't use default
           ==> do nothing 
        }
     }
  } // end for-all-Attrs

  // do this recursively
  for ( all child elements of Element )
  {
    childElement.normalizeNamespaces()
  }
} // end Element.normalizeNamespaces

Scope of a Binding[top]

Scope of a Binding

NOTE:
This section is informative.

An element's prefix/namespace URI pair is said to be within the scope of a binding if its namespace prefix is bound to the same namespace URI in the [in-scope namespaces] defined in [InfoSet].

As an example, the following document is loaded in a DOM tree:

<root>
  <parent xmlns:ns="http://www.example.org/ns1"
          xmlns:bar="http://www.example.org/ns2">
    <ns:child1 xmlns:ns="http://www.example.org/ns2"/>
  </parent>
</root>

In the case of the child1 element, the namespace prefix and namespace URI are within the scope of the appropriate namespace declaration given that the namespace prefix ns of child1 is bound to http://www.example.org/ns2.

Using the method Node.appendChild, a child2 element is added as a sibling of child1 with the same namespace prefix and namespace URI, i.e. "ns" and "http://www.example.org/ns2" respectively. Unlike child1 which contains the appropriate namespace declaration in its attributes, child2's prefix/namespace URI pair is within the scope of the namespace declaration of its parent, and the namespace prefix "ns" is bound to "http://www.example.org/ns1". child2's prefix/namespace URI pair is therefore not within the scope of a binding. In order to put them within a scope of a binding, the namespace normalization algorithm will create a namespace declaration attribute value to bind the namespace prefix "ns" to the namespace URI "http://www.example.org/ns2" and will attach to child2. The XML representation of the document after the completion of the namespace normalization algorithm will be:

<root>
  <parent xmlns:ns="http://www.example.org/ns1"
          xmlns:bar="http://www.example.org/ns2">
    <ns:child1 xmlns:ns="http://www.example.org/ns2"/>
    <ns:child2 xmlns:ns="http://www.example.org/ns2"/>
  </parent>
</root>

To determine if an element is within the scope of a binding, one can invoke Node.lookupNamespaceURI, using its namespace prefix as the parameter, and compare the resulting namespace URI against the desired URI, or one can invoke Node.isDefaultNamespaceURI using its namespace URI if the element has no namespace prefix.

Conflicting Namespace Declaration[top]

Conflicting Namespace Declaration

NOTE:
This section is informative.

A conflicting namespace declaration could occur on an element if an Element node and a namespace declaration attribute use the same prefix but map them to two different namespace URIs.

As an example, the following document is loaded in a DOM tree:

<root>
  <ns:child1 xmlns:ns="http://www.example.org/ns1">
    <ns:child2/> 
  </ns:child1>   
</root>

Using the method Node.renameNode, the namespace URI of the element child1 is renamed from "http://www.example.org/ns1" to "http://www.example.org/ns2". The namespace prefix "ns" is now mapped to two different namespace URIs at the element child1 level and thus the namespace declaration is declared conflicting. The namespace normalization algorithm will resolved the namespace prefix conflict by modifying the namespace declaration attribute value from "http://www.example.org/ns1" to "http://www.example.org/ns2". The algorithm will then continue and consider the element child2, will no longer find a namespace declaration mapping the namespace prefix "ns" to "http://www.example.org/ns1" in the element's scope, and will create a new one. The XML representation of the document after the completion of the namespace normalization algorithm will be:

<root>
  <ns:child1 xmlns:ns="http://www.example.org/ns2">
    <ns:child2  xmlns:ns="http://www.example.org/ns1"/> 
  </ns:child1>   
</root>

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Table of contents

Appendices

B.1 Namespace Normalization

Scope of a Binding[top]

Conflicting Namespace Declaration[top]