Placement Widget
From Synfig Studio :: Documentation
Draft
The "Placement Widget" (or DockDropArea) is a graphical control element composed of four buttons helping to organize the placement of the Panels composing the synfigstudio's interface.
Here a screenshot of the control is missing
Those buttons are the places to drop down the panels tabs to arrange them in different configurations. Subdivide the panel it belongs to into two panels and the dragged tab would be in the relative place where you drop the tab over those four buttons.
Video showing the use of the "Placement Widget".