It's also nice to see these features implemented in wxWidgets:

• Add wxRegexValidator for regular expression validations.
• Make wxValidators generate events to report validation failure/success. Or...
• Add wxValidatorProxy and let users customize validation behaviours:
  • Use wxRichToolTip to show error messages instead of the default message box.
  • Choose to revert to the previous valid value instead of clamping the value.
• Do not generate wxEVT_TEXT event while the wxDialog/wxPanel is initialized due to calling SetValue() in the process of transferring data to window (TransferToWindow())

wxValidatorProxy might look like this:

class wxValidatorProxy
{
public:
    wxValidatorProxy() = default;
    virtual ~wxValidatorProxy() = default;

    // Return false to prevent default processing to take place

    virtual bool OnSuccess() const { return true; }
    virtual bool OnFailure(/*...*/) const { return true; }
    virtual bool OnIncompleteEntry(/*...*/) const { return true; }
};

Thanks for any other ideas!