Managing tool boxes in Gimp
This explains in simple language how to manage the tool boxes in Gimp. (Mostly as asides, it also critiques the user interface, to help you understand.)
First, terminology. Gimp calls them "Dockable Dialogs". Here I call them tool boxes. (programmers distinguish tool boxes, where you choose a tool then hit something with it, from list boxes, where you choose something, for example a layer, and pull down a menu for it, or just choose something to activate or select it. Gimp reserves the word "Toolbox" for the window of drawing tools like the Pencil tool, and it is NOT a lower-case tool box.)
Docks. There is not "a dock". You can have many docks. It is best to think of docks as rafts, that is, tool boxes lashed together inside a window. You dock tool boxes to each other to make a raft. (A window that holds a raft has controls for docking, but has no frame or outline that distinguishes it as a raft.)
What rafts look like. A raft of tool boxes is in a window, separate from any image window. The tool boxes in a raft are either tabbed, or adjacent (one north of another), or both. A window that holds a raft is titled with a list of the tool boxes in the raft. (Except that the Toolbox window always says just "Toolbox" even if it is a raft with other tool boxes.) A raft always contains these (obscure) controls: a dock bar near the top, a dock bar at the bottom, and a "Tab Menu button" near the top right.
Cloning tool boxes: there is not "a toolbox" of each kind: the same toolbox can have clones visible (even with clones together in the same raft!) All clones of a toolbox present the same information, that is, they stay synced. (I haven't figured out the conditions when a clone will be created versus an existing tool box brought to the top. This might be a bug.)
Controls for docking.
1) The "Windows>Recently Closed Docks": to open recently closed rafts (but only those that had more than one toolbox)
2) "Windows>Dockable Dialogs" menus : to open toolboxes inside a new raft, or bring them to the top
3) "dock bars" : a target for drag-and-dropping tool boxes
4) other places to drop toolboxes
5) "dock handle areas" : a grab place to drag a tool box from
6) other places to drag toolboxes from
7) "Tab Menu" buttons : a menu in a tabbed raft to control the tool boxes there, or add tool boxes
"Windows>Recently Closed Docks": This shows you rafts (windows) of tool boxes that you recently closed. Choose one to reopen it, as it was. (It should just be "Window>Open Recent" like "File>Open Recent". Recently closed, solitary toolbox windows aren't listed. By that logic, a dock is not a dock until it has more than one toolbox in it, which is paradoxical. )
"Windows>Dockable Dialogs": This lists all the tool boxes that Gimp provides. Choosing one opens it in a new raft OR brings it to the top if it is already open OR creates a clone if it is already open. (The Gimp User Manual erroneously says it will bring it to the top if it is already in a raft. In my experience, it sometimes opens a clone in a new raft, sometimes opens a clone in an existing raft, and sometimes brings it to the top.)
Dock bars: A dock bar is a sliver of a rectangle, one at the top and one at the bottom of a raft. It is a target for drag-and-drop. Dragging a toolbox to a top dock bar puts the toolbox in a tab in the raft. Dragging a toolbox to a bottom dock bar puts the toolbox adjacent (south of) the toolboxes already in the raft. A tooltip tells you it is a target for drag-and-drop. It does highlight when you drag a toolbox over it. (The dock bar is too small for most users to notice, it looks like a separator bar.)
Other places to drag and drop toolboxes: You can also drop a toolbox on top of another toolbox. The dropped toolbox becomes tabbed with the target toolbox. You can drag to either the tab or the body of a toolbox. (Except: when a toolbox is in the Toolbox window, you can only drag to its tab, and not to its body!)
Dock handle areas: The displayed name in a toolbox, like "Layer", is one place where you can start drag-and-drop. The cursor changes to a hand icon when you CAN begin a drag, and the cursor becomes a small box with the name of the tool box as you drag. (!!! Note the banner of the window of a raft will also be the name of the toolbox(es) in the raft, but you can't drag a toolbox from the banner, only the window.)
Other places to drag toolboxes from: you can drag a toolbox starting from its tab if the tab is on top. (The tooltip says "Open..." but it should say "Open or drag...". Also, as you mouseover a tab, the cursor remains the pointer icon, and doesn't change to a hand icon, even though you can start a drag.)
Tab menu button: This a button with a left arrow icon, to the right of the name or tabs for every tool box. Clicking on it brings up a menu. All but the top menu item affect the raft. For example, let you add or delete tool boxes, or change the appearance of the raft. The top menu item is NOT about the raft, but about the tool box. For example, for the Layers tool box, it brings up the Layers menu.
The usual rafts: The Toolbox window can be a raft. (But the name of the window never changes to list the tool boxes in the raft.) The Devices windows can be a raft. You can create as many other rafts as you want.
Casual readers can skip the following critique of annoyances.
Special case: Tool Options toolbox. On a newly installed Gimp, this toolbox is open rafted underneath the tools in the "Toolbox" window. This is the natural place for it, but you CAN move it elsewhere, and it might persist there across invocations of Gimp.
Special case: the dock bar at the bottom of the Toolbox window. This dock bar grows larger and displays "You can drop dockable dialogs here" if the Toolbox window is resized larger. This differs from other dock bars (which I have yet to see resize to other than a sliver.)
Special case: the dock bar near the top of the Toolbox window. It is below the tools, not at the top of the window like other rafts.
Special case: Device Status toolbox. It appears in Windows>Dockable Dialogs, but it is not draggable to any other raft, but always appears in the "Devices" window. That raft will hold other toolboxes, but the Device Status toolbox can't leave the raft of the "Devices" window.
Special case: some toolboxes are NOT named as in the Windows>Dockable Dialogs menu. For example, the "Tool Options" toolbox is named for the current tool (for example is named "Paint" but should be named "Tool Options: Paint". For another example, the "Colors" tool box is named "FG/BG Colors" when it opens.)
You can't drag a raft (the window containing the raft) into another raft to combine them. You must drag toolboxes one at a time from raft to raft.
Hidden new tool box gotcha: a newly opened toolbox in its own raft can be hidden behind other windows! This might depend on Edit>Preferences>Window Management>Window Manager Hints>Hints for Other Docks ?
Closing the Toolbox: closes the Gimp application. It is a raft that closes differently from other rafts.
The dock versus raft metaphor. Some docks have slips. Only one boat can usually be put in each slip. A long dock might not have slips defined, in which case many boats can be docked, but only generally in the configuration the dock defines (a long row.) A docked boat is moored (fixed), but can later move elsewhere. Docks usually don't move. Docks with slips often have boats assigned to a slip. Long, public docks might allow boats anywhere. Rafted boats are tied together in a variety of configurations, as many boats as you want. A raft of boats is often moored to an anchor, but can move. The Apple dock is like a long dock. The Gimp dock concept is more like a set of rafts.