Tk supports two different kinds of windows: internal windows and top-level windows. An internal window is an interior window of a Tk application, such as a scrollbar or menu bar or button. A top-level window is one that is created as a child of a screen's root window, rather than as an interior window, but which is logically part of some existing main window. Examples of top-level windows are pop-up menus and dialog boxes.
New windows may be created by calling Tk_CreateWindow. If the topLevScreen argument is NULL, then the new window will be an internal window. If topLevScreen is non-NULL, then the new window will be a top-level window: topLevScreen indicates the name of a screen and the new window will be created as a child of the root window of topLevScreen. In either case Tk will consider the new window to be the logical child of parent: the new window's path name will reflect this fact, options may be specified for the new window under this assumption, and so on. The only difference is that new X window for a top-level window will not be a child of parent's X window. For example, a pull-down menu's parent would be the button-like window used to invoke it, which would in turn be a child of the menu bar window. A dialog box might have the application's main window as its parent.
Tk_CreateAnonymousWindow differs from Tk_CreateWindow in that it creates an unnamed window. This window will be manipulable only using C interfaces, and will not be visible to Tcl scripts. Both interior windows and top-level windows may be created with Tk_CreateAnonymousWindow.
Tk_CreateWindowFromPath offers an alternate way of specifying new windows. In Tk_CreateWindowFromPath the new window is specified with a token for any window in the target application (tkwin), plus a path name for the new window. It produces the same effect as Tk_CreateWindow and allows both top-level and internal windows to be created, depending on the value of topLevScreen. In calls to Tk_CreateWindowFromPath, as in calls to Tk_CreateWindow, the parent of the new window must exist at the time of the call, but the new window must not already exist.
The window creation procedures do not actually issue the command to X to create a window. Instead, they create a local data structure associated with the window and defer the creation of the X window. The window will actually be created by the first call to Tk_MapWindow. Deferred window creation allows various aspects of the window (such as its size, background color, etc.) to be modified after its creation without incurring any overhead in the X server. When the window is finally mapped all of the window attributes can be set while creating the window.
The value returned by a window-creation procedure is not the X token for the window (it cannot be, since X has not been asked to create the window yet). Instead, it is a token for Tk's local data structure for the window. Most of the Tk library procedures take Tk_Window tokens, rather than X identifiers. The actual X window identifier can be retrieved from the local data structure using the Tk_WindowId macro; see the manual entry for Tk_WindowId for details.
Tk_DestroyWindow deletes a window and all the data structures associated with it, including any event handlers created with Tk_CreateEventHandler. In addition, Tk_DestroyWindow will delete any children of tkwin recursively (where children are defined in the Tk sense, consisting of all windows that were created with the given window as parent). If tkwin is an internal window, then event handlers interested in destroy events are invoked immediately. If tkwin is a top-level or main window, then the event handlers will be invoked later, after X has seen the request and returned an event for it.
If a window has been created but has not been mapped, so no X window exists, it is possible to force the creation of the X window by calling Tk_MakeWindowExist. This procedure issues the X commands to instantiate the window given by tkwin.