Float

A window pane is a dockable window. When you "dock" a window you position (or 'pin') it along the edge of another window or pane.

When you "float" a docked window pane, you move it so that it is no longer positioned along the edge of another window or pane.

To "float" a tabbed window (for example the Properties pane) right-click on the window tab and select Float from the right-click menu.

Alternatively, click and drag the title bar of the pane to float it in the Design Window.

The pane can now be docked like any other window pane. See: Dock

To make the Properties pane a tabbed pane again, simply right-click the down arrow button on the title bar and choose Auto Hide: