NAME                                                              (V36)
	CreateBehindHookLayer -- Create a new layer behind all existing layers,
	                         using supplied callback BackFill hook.

    SYNOPSIS
	result = CreateBehindHookLayer(li,bm,x0,y0,x1,y1,flags,hook,[,bm2])
	d0                             a0 a1 d0 d1 d2 d3 d4    a3   [ a2 ]

	struct Layer *CreateBehindHookLayer(struct Layer_Info *, struct BitMap *,
	    LONG, LONG, LONG, LONG, LONG, struct Hook *, ... );

    FUNCTION
	Create a new Layer of position and size (x0,y0)->(x1,y1)
	Make this layer of type found in flags.
	Install Layer->BackFill callback Hook.
	If SuperBitMap, use bm2 as pointer to real SuperBitMap,
	and copy contents of Superbitmap into display layer.
	If this layer is a backdrop layer then place it behind all
	other layers including other backdrop layers. If this is
	not a backdrop layer then place it behind all nonbackdrop
	layers.

	Note: when using SUPERBITMAP, you should also set LAYERSMART flag.

    INPUTS
	li - pointer to LayerInfo structure
	bm - pointer to common BitMap used by all Layers
	x0,y0 - upper left hand corner of layer
	x1,y1 - lower right hand corner of layer
	flags - various types of layers supported as bit sets.
	        (for bit definitions, see graphics/layers.h )
	hook -  Layer->BackFill callback Hook (see InstallLayerHook())

	        If hook is LAYERS_BACKFILL, the default backfill is
	        used for the layer.  (Same as pre-2.0)

	        As of V39:
		If hook is LAYERS_NOBACKFILL, the layer will not be
	        backfilled (NO-OP).

	bm2 - pointer to optional Super BitMap

    RESULTS
	result - pointer to Layer structure if successful
	         NULL if not successful

    BUGS

    SEE ALSO
	InstallLayerHook(), DeleteLayer(), graphics/layers.h, graphics/clip.h,
	graphics/gfx.h, utility/hooks.h