From Synfig Studio :: Documentation
OutDated (more or less remplaced by Panels)
A Dock dialog consists of one or more Dock Panels.
Names of all dock tabs resided in a dialog are listed in title of that dialog.
Tabs can be added or removed from a Dock dialog by dragging them, from the dock tab, onto other Dock dialogs or out from it current Dock dialog. If released outside any other Dock a new dock is created with the released tab.
Tabs can also be rearranged within the Dock dialog by dragging them past each other.