!! +exec+ +var+ +string+
$lst_tit nonempty$lst_titend$type_both
  $lst_alias non_empty
  $(lst_syntax)nonempty $emph obj$emphend $emph content$emphend</tt>
  $lst_mean $emph obj$emphend 可以是 $emph item$emphend 或 $emph line$emphend.
  $emph content$emphend 内的非空项或行将被提取出来.
  
