Please help me to clarify the concepts of some specific terms about imgui

[ocornut]

Thanks for asking. It may be a good idea that we create an officially annotated picture.

Does green rect is Platform Decorations?

Yes, but it also technically include the window border and resizing behavior when clicking on that border.
Resizing from platform window border uses a different code path than resizing from imgui resize border/corner (e.g. clicking on bottom right of "Hello, World!" window).

Does red rect are Docking Decorations?

Yes.

Does orange rect are Host Windows?

Yes.

Does "Floating" Dock Node's size always same as it's Host Window?

Yes, the root dock node is. If you make the Debugger/Demo split float externally, the root dock node is same same as host window, but each child dock is roughly half of the size.

Where is the Central Node?
Where is the Dockspace?

There's none in that screenshot.
Presumably because DockSpaceOverViewport() or DockSpace() isn't called.
DockSpace created a docking node attached inside a window.

Central Node is not technically distinguishable from other nodes (which has been a design problem and source of confusion).
In an empty DockSpace the only node would be the central node. If you dock another window to the right of the central node, the central node will stay the one on the left. It's basically a property that's held in a single node.
One aspect of this property is that it allow the node to stay visible even if it is empty (whereas other one would hide/collapse).
I think the concept of central node will be removed eventually, it's causing too many issues, may need to use another technique to specify resizing/emptying behavior.

[JTtNinjaCode]

Thank you a lot!