-/* This will write a snapshot of the screen image into the given window.
- Beware that the colormap of the window may also be changed (to match
- the bits that were drawn.)
+/* This will write an image onto the given Drawable.
+ The Drawable (arg 3) may be a Window or a Pixmap.
+
+ The Window must be the top-level window. The image *may or may not*
+ be written to the window, though it will definitely be written to
+ the drawable. It's fine for args 2 and 3 to be the same window, or
+ for arg 2 to be a Window, and arg 3 to be a Pixmap.
+
+ The loaded image might be from a file, or from a screen shot of the
+ desktop, or from the system's video input, depending on user
+ preferences.
+
+ Many colors may be allocated from the window's colormap.