code: def param(name, value_info, is_required=True, label=None, desc=None):
      
      _annotate("param", name, value_info, is_required=is_required,
                label=label, desc=desc)
docs: Annotate a parameter of the action being defined.
      @param name: name of the parameter defined.
      @type name: unicode or str
      @param value_info: the parameter value information.
      @type value_info: value.IValueInfo
      @param is_required: if the parameter is required or optional.
      @type is_required: bool
      @param label: the parameter label or None.
      @type label: str or unicode or None
      @param desc: the parameter description or None.
      @type desc: str or unicode or None