With the Appearance Manager, the look of a window frame--not just its color, but its size and shape--may vary from appearance to appearance. Because the size of a window frame can vary, the total dimensions of a window (that is, the window's structure region) may also vary, causing the window's spatial relationship to the rest of the screen to change.
Additionally, the elements of a window frame may vary in their size, shape, or position. For example, some appearances may allow the window to be resized from any corner, not just the bottom right, and as a result, when the user drags the size box around the screen, the window may move on the screen and not merely change size.
Your application can best accommodate variable window dimensions by using the functions provided by the Mac OS 8.5 Window Manager to size and position your windows, rather than via constant dimensions. Using these functions allows your application to avoid maintaining its own table of window definition IDs and their various border dimensions.
The Mac OS 8.5 Window Manager provides the following functions for working with the size and position of windows. See Positioning a Window on the Desktop and Resizing a Window for a discussion of these functions.