anchor.diff:  
   
   [[long-only-val]]
  -===== Long only with value
  +==== Long only with value
   
   ----
   int CheckArg::add(const std::string &lopt, const std::string &help, bool has_val=false);            // <1>
  
positive.code: TIP: See the <<callbacks>> section of this document for more info on callbacks.
  
  
  ===== Automatic help
  
  [NOTE]
  ====
  
negative.code: 
  
  
  ==== Long only
  
  ----
  int CheckArg::add(const std::string &lopt, const std::string &help);    // <1>
  