An embedded window is simply a window (child window) within the topic window. Embedded windows do not have any standard window elements; they are just rectangular regions. Users cannot minimize, maximize, or resize an embedded window, and Help authors cannot use embedded windows as hot spots. However, you can include hot spots in an embedded window that are controlled by the DLL, but users will not be able to use the keyboard equivalents to access the hot spots. That is because embedded windows cannot receive the input focus which means they cannot process keystrokes. So, you should not place anything in an embedded window that requires keyboard input from users.
Windows Help positions the embedded window using the justification character (left, right, or character) specified by the author in the embedded window reference. The embedded window DLL is expected to display the information in the window and resize the window appropriately. Help expects the window size to remain fixed as long as the topic is displayed. The window element and DLL determine the size and content of the embedded window, and Help arranges the other elements of the topic around the embedded window.
Embedded windows are supported by DLLs that have specific components required by the embedded window interface. Developers familiar with DLL programming can write DLLs to support new user-interface or display elements not available in the standard Windows Help feature set. For example, developers can create a DLL to display 256-color bitmaps in an embedded window. For a discussion of the embedded window interface and for a description of a sample DLL, see Chapter 20, “Writing DLLs for Windows Help.”.
Windows Help displays embedded windows only when necessary—while the topic containing the embedded window is being displayed. However, an embedded window may exist while it is not being displayed (if the topic scrolls past the embedded window, for example). Because it is part of a specific topic, an embedded window goes away when the user displays a different topic.