docs: private String stem(int del, String add, String affix) {
      int stem_length = yylength() - del;
      int i = 0;
  
      String result=yytext().substring(0,stem_length); 
  
      if (option(change_case)) { result=result.toLowerCase(); }
      if (!(add.length()==0)) result+=add;
  
      if(option(print_affixes)) { result+=("+"+affix); }
  
      return result;
    }