| rx
	  (PLFLT, input)	    Input relative device coordinate (ranging from 0. to 1.) for the
	    x coordinate.
	  ry
	  (PLFLT, input)	    Input relative device coordinate (ranging from 0. to 1.) for the
	    y coordinate.
	  wx
	  (PLFLT *, output)	    Pointer to the returned world coordinate for x corresponding
	    to the relative device coordinates
	    rx and
	    ry.
	  wy
	  (PLFLT *, output)	    Pointer to the returned world coordinate for y corresponding
	    to the relative device coordinates
	    rx and
	    ry.
	  window
	  (PLINT *, output)	    Pointer to the returned last defined window index that corresponds to the
	    input relative device coordinates (and the returned world
	    coordinates).  To give some background on the window index,
	    for each page the initial window index is set to
	    zero, and each time plwindis called within the page, world
	    and device coordinates are stored for the window and the window
	    index is incremented.  Thus, for a simple page layout with
	    non-overlapping viewports and one window per viewport,
	    window corresponds to
	    the viewport index (in the order which the viewport/windows
	    were created) of the only viewport/window corresponding to
	    rx and
	    ry.  However, for
	    more complicated layouts with potentially overlapping viewports
	    and possibly more than one window (set of world coordinates) per
	    viewport, window
	    and the corresponding output world coordinates
	    corresponds to the last window created that fulfils the criterion
	    that the relative device coordinates are inside it.  Finally, in
	    all cases where the input relative device coordinates are not
	    inside any viewport/window, then
	    window is set to -1.
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