Sigh…

type

  Default = class(TCustomAttribute)

  public

    Value: T;

    constructor Create(const aValue: T);

   function AsString:String;

  end;

…

  TMyEdit = class(TEditor)

  protected

    [Default(200)] // [dcc32 Error]: E2029 ‘]’ expected but ‘<' found

    SupplierNo: TIntegerEdit;

    //…

 end;

#halfbaked