@Mark-J Thanks, yes, cmds.dockControl works in 2017, but it has very limited docking areas, I think only far-left and far-right. Not even alongside Attribute editor, outside of that layout.
Ah, I see, I also always thought that staying with cmds should provide better support and easier upgrades from version to version, I never thought there’d be some breaking change there. But as it turned out using QT seems to be a better bet in the end.