Oh, sorry. Though the new docking system’s tabs looked just like it off of memory.
Use UIListLayout. Below, I have a couple of TextButtons parented with a UIListLayout to a Frame. I’ve set the SortOrder property on the UIListLayout to Name. This orders the TextButtons by name.
For the coding side, create a script that constantly changes the name of the focused tab to the X axis of mouse’s position relative to the plugin widget.
The only downside to this is that the tabs instantly snap into position and there is no animation to them.