You can dock several panels together into a single floating window which you can then move around.
This is especially useful when you're setting up your editors on a second monitor. For example, you can dock the Attribute Editor and Channel Box together and keep them on another monitor to maximize the working space in the view panel.
Drag another panel onto an edge of the panel in the floating window.
To create a tab deck if one does not exist yet, drag the panel to the upper-left corner of the panel in the target window until a blue triangle appears, then release the mouse button.