int idx;

  if( argc!=3 ){
    return Th_WrongNumArgs(interp, "append_field FIELD STRING");
  }
  if( g.thTrace ){
    Th_Trace("append_field %#h {%#h}<br>\n",
              argl[1], argv[1], argl[2], argv[2]);
              TH1_LEN(argl[1]), argv[1], TH1_LEN(argl[2]), argv[2]);
  }
  for(idx=0; idx<nField; idx++){
    if( memcmp(aField[idx].zName, argv[1], argl[1])==0
        && aField[idx].zName[argl[1]]==0 ){
    if( memcmp(aField[idx].zName, argv[1], TH1_LEN(argl[1]))==0
        && aField[idx].zName[TH1_LEN(argl[1])]==0 ){
      break;
    }
  }
  if( idx>=nField ){
    Th_ErrorMessage(g.interp, "no such TICKET column: ", argv[1], argl[1]);
    return TH_ERROR;
  }