code: public void addNsBinding(String prefix, String uri)
      {
          // Unbind? (xml 1.1...)
          if ((uri == null) || (uri.length() == 0)) {
              uri = null;
          }
  
          // Default ns declaration?
          if ((prefix == null) || (prefix.length() == 0)) {
              prefix = null;
              mCurrElement.mDefaultNsURI = uri;
          }
          mNamespaces.addStrings(prefix, uri);
      }
docs: Callback method called by the namespace default provider. At
  this point we can trust it to only call this method with somewhat
  valid arguments (no dups etc).