NAME
        InstallClipRegion -- Install clip region in layer

    SYNOPSIS
        oldclipregion = InstallClipRegion( l,  region )
        d0                                 a0  a1

        struct region *installclipregion( struct layer *, struct region *);

    FUNCTION
        Installs a transparent Clip region in the layer. All
        subsequent graphics calls will be clipped to this region.
        You MUST remember to call InstallClipRegion(l,NULL) before
        calling DeleteLayer(l) or the Intuition function closewindow()
        if you have installed a non-NULL ClipRegion in l.

    INPUTS
        l - pointer to a layer
        region - pointer to a region

    RESULTS
        oldclipregion - The pointer to the previous ClipRegion that
            was installed. Returns NULL if no previous ClipRegion installed.

            Note: If the system runs out of memory while computing the
                resulting ClipRects the LAYERS_CLIPRECTS_LOST bit will
                be set in l->Flags.

    BUGS
        If the system runs out of memory during normal layer operations,
        the cliprect list may get swept away and not restored.
        As soon as there is enough memory and the layer library
        gets called again the cliprect list will be rebuilt.

    SEE ALSO
        beginupdate() endupdate(),
        graphics/layers.h, graphics/clip.h, graphics/regions.h