-Returns the value of a system metric, or -1 if the metric is not
-supported on the current platform.
+Returns the value of a system metric, or -1 if the metric is not supported on the current system.
+The value of {\it win} determines if the metric returned is a global value or
+a \helpref{wxWindow}{wxwindow} based value, in which case it might determine the widget, the
+display the window is on, or something similar. The window given should be as close to the
+metric as possible (e.g a wxTopLevelWindow in case of the wxSYS\_CAPTION\_Y metric).