In the X Window System, window managers largely control how an application's windows behave. Applications inform the currently active window manager of important facts and hints about a window by storing properties of certain names and types on that window. Each window manager determines what it will do with this information by itself; your application does not have any control over it.
X does establish many conventions for what window managers are expected to do, and you are encouraged to use those conventions. However, at this stage in the development of the X Window System, most window managers do not follow all these conventions. Keep this in mind when you are testing code that makes demands of window managers: your test may be failing due to no fault in your program, but simply because the window manager you are using does not support the feature you require.
All interaction with the window manager is done through window properties. As described above (see pxl-win-atts), window properties are window attributes of the form
property(Name,Value)
These can be set with create_window and put_window_attributes.