When registering options in an initialization section, with a duplicate short name, this can cause a 217 runtime error due to an exception being raised before sysutils has initialized. Investigating.

Allow the user to implement his own validation implementation i.e. by implementing an OnValidation event as TValidationEvent = function(aOption: IOptionDefinition; const Value: string): boolean

Unnamed parameters should also have a name, so they can be explained in the usage string

When looking into #16 I found out that PrintUsage crashes when the description is empty

                   if opt.HasValue then
                      s := s + FNameValueSeparator + '<' + opt.LongName + '>';
                    if opt.AllowMultiple then
                      s := s + ' +'
                    else
                      s := s + '  ';
                    s := PadRight(s, FDescriptionTab);
-->                 s := s + descStrings[0];  <-- Exception occurs here
                    proc(s);
                    numDescStrings := Length(descStrings);
                    if numDescStrings > 1 then
                    begin
                      for i := 1 to numDescStrings -1 do
                      begin
                        s := PadLeft(descStrings[i], FDescriptionTab);
                        proc(s);
                      end;
                      proc('');
                    end;

The hidden attribute introduced in ac9c738 is no longer functional since a long time. It is still there, but never checked. I didn't try to find out in which commit it was removed.

In VSoft.CommandLine.OptionDef.pas, under tkFloat: in TOptionDefinition<T>.Invoke, StrToFloat is called, but StrToFloat is locale specific.

This means that on most European machines, StrToFloat will assume ',' as a decimal separator and not '.'. That might not work well for scripts that use a program using this command line parser.

Now, I cannot find a simple method like Str (which for the reverse case always uses '.' as decimal separator, whereas FloatToStr would always use the locale), so you need to supply a TFormatSettings with DecimalSeparator set to '.' as its second argument.

When registering an option it would be handy to be able to define a default value for the parameter, which will also be mentioned in the Usage: string

I just had a need to be able to register sets of options, which are context sensitive based on another option, e.g

mytool commandA [command A options]
mytool commandB [command B options]

Open to suggestions on how to implement this.

In the master branch in vsoft.commandline.options.pas at line 348 the check if numDescStrings > 1 is probably wrong and the first option help text is never displayed in print usage.

Changing the check with if numDescStrings > 0 correctly works.