code: public String addExtent(Properties attributes) throws XDocletException
      {
          String name = attributes.getProperty(ATTRIBUTE_NAME);
  
          if (!_model.hasClass(name))
          {
              throw new XDocletException(Translator.getString(XDocletModulesOjbMessages.class,
                                         XDocletModulesOjbMessages.COULD_NOT_FIND_TYPE,
                                         new String[]{name}));
          }
          _curClassDef.addExtentClass(_model.getClass(name));
          return "";
      }
docs: Adds an extent relation to the current class definition.
  
  @param attributes            The attributes of the tag
  @return                      An empty string
  @exception XDocletException  If an error occurs
  @doc.tag                     type="content"
  @doc.param                   name="name" optional="false" description="The fully qualified name of the extending
  class"