private String parseTokenChecked(String str, int ichStart, int ichMax) {
    int ich = ichStart;
    char ch;
    while (ich < ichMax && ((ch = str.charAt(ich)) == ' ' || ch == '\t'))
      ++ich;
    int ichNonWhite = ich;
    while (ich < ichMax && ((ch = str.charAt(ich)) != ' ' && ch != '\t'))
      ++ich;
    ichNextParse = ich;
    if (ichNonWhite == ich)
      return null;
    return str.substring(ichNonWhite, ich);
  }