Index: trunk/src/data.c
===================================================================
--- trunk/src/data.c	(revision 725)
+++ trunk/src/data.c	(revision 726)
@@ -71,22 +71,36 @@
 }
 
 
-void camv_layer_append_to_design(camv_design_t *camv, camv_layer_t *layer)
+long camv_layer_append_to_design(camv_design_t *camv, camv_layer_t *layer)
 {
+	long res = -1;
+
 	assert(layer->parent == NULL);
 	if (camv->grp_load) {
 		if (camv->grp_idx_last < 0) {
 			camv->grp_idx_last = camv->layers.used;
+			res = camv->layers.used;
 			vtp0_append(&camv->layers, layer);
 		}
-		else
+		else {
 			vtp0_insert_len(&camv->layers, camv->grp_idx_last, &layer, 1);
+			res = camv->grp_idx_last;
+		}
 	}
-	else
+	else {
+		res = camv->layers.used;
 		vtp0_append(&camv->layers, layer);
+	}
 	layer->parent = camv;
+	return res;
 }
 
+long camv_sublayer_append_after(camv_design_t *camv, camv_layer_t *layer, long idx)
+{
+	idx++;
+	vtp0_insert_len(&camv->layers, idx, &layer, 1);
+	return idx;
+}
 
 camv_layer_t *camv_layer_by_name(camv_design_t *camv, const char *name, int alloc)
 {
Index: trunk/src/data.h
===================================================================
--- trunk/src/data.h	(revision 725)
+++ trunk/src/data.h	(revision 726)
@@ -47,6 +47,11 @@
 	vtp0_t layers; /* to camv_layer_t */
 	int lysel;     /* layer idx (lid) of the currently selected layer */
 	camv_rtree_box_t bbox;
+
+	/* for loaders */
+	struct {
+		long ly;
+	} loader;
 };
 
 struct camv_layer_s {
@@ -75,8 +80,13 @@
    non-existing layer if alloc is non-zero; appends to design automatically */
 camv_layer_t *camv_layer_by_name(camv_design_t *camv, const char *name, int alloc);
 
-void camv_layer_append_to_design(camv_design_t *camv, camv_layer_t *layer);
+/* Returns index of the new layer (useful for camv_sublayer_append_after()) */
+long camv_layer_append_to_design(camv_design_t *camv, camv_layer_t *layer);
 
+/* Appends a (typically hidden) sublayer after the last layer of the group
+   at idx; returns new idx for appending more sublayers */
+long camv_sublayer_append_after(camv_design_t *camv, camv_layer_t *layer, long idx);
+
 /* Invent a layer color for a main layer that has non set explicitly */
 void camv_layer_invent_color(camv_design_t *camv, camv_layer_t *layer);