[quote=420257:@Pedro Ivan Tellez Corella]Those are called Layout Containers, they are not new, some tool had them for decades. There are some requests to be added to xojo, but, since they dont even add a datetime control, Layout Containers seems not something in the near future of xojo.
Of course, you can do it manually, lots of code in the resizing event of the container control.
That is A window splitter[/quote]
I have used IMsplitter in some of my Mac Apps and its solid for my splitter needs as @Beatrix Willius has above.
“My Notes” Container on this image is using the IM Splitter for my listbox and textarea controls. Its hard to see on this PIC but the vertical white line 2 or 3 px wide is the splitter.