Polishing: add comments.

                        TABLE)

    mem_root            MEM_ROOT for parameters allocation

    parameters          parameters description

    required            number of required parameters in above list

    required            number of parameters in the above list. If the file

                        contains more parameters than "required", they will

                        be ignored. If the file contains less parameters

                        then "required", non-existing parameters will

                        remain their values.

    hook                hook called for unknown keys

    hook_data           some data specific for the hook

      }

    }

  }

  /*

    NOTE: if we read less than "required" parameters, it is still Ok.

    Probably, we've just read the file of the previous version, which

    contains less parameters.

  */

  DBUG_RETURN(FALSE);

}