Index: trunk/src/libcschem/cnc_arc.c
===================================================================
--- trunk/src/libcschem/cnc_arc.c	(revision 572)
+++ trunk/src/libcschem/cnc_arc.c	(revision 573)
@@ -35,12 +35,12 @@
 {
 	csch_arc_t *arc;
 
-	arc = htip_get(&sheet->id2obj, oid);
+	arc = htip_get(&parent->id2obj, oid);
 	if (arc != NULL)
 		return NULL;
 	arc = calloc(sizeof(csch_arc_t), 1);
 
-	csch_cobj_init(&arc->hdr, sheet, oid, CSCH_CTYPE_ARC, CSCH_INVALID_OID);
+	csch_cobj_init(&arc->hdr, sheet, parent, oid, CSCH_CTYPE_ARC);
 	return arc;
 }
 
@@ -50,9 +50,9 @@
 	free(arc);
 }
 
-csch_arc_t *csch_arc_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_arc_t *csch_arc_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid)
 {
-	csch_arc_t *arc = htip_get(&sheet->id2obj, oid);
+	csch_arc_t *arc = htip_get(&grp->id2obj, oid);
 	if ((arc != NULL) && (arc->hdr.type != CSCH_CTYPE_ARC))
 		return NULL;
 	return arc;
Index: trunk/src/libcschem/cnc_arc.h
===================================================================
--- trunk/src/libcschem/cnc_arc.h	(revision 572)
+++ trunk/src/libcschem/cnc_arc.h	(revision 573)
@@ -43,6 +43,6 @@
 
 csch_arc_t *csch_arc_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_arc_free(csch_arc_t *arc);
-csch_arc_t *csch_arc_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_arc_t *csch_arc_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid);
 
 #endif
Index: trunk/src/libcschem/cnc_bitmap.c
===================================================================
--- trunk/src/libcschem/cnc_bitmap.c	(revision 572)
+++ trunk/src/libcschem/cnc_bitmap.c	(revision 573)
@@ -34,12 +34,12 @@
 {
 	csch_cbitmap_t *bitmap;
 
-	bitmap = htip_get(&sheet->id2obj, oid);
+	bitmap = htip_get(&parent->id2obj, oid);
 	if (bitmap != NULL)
 		return NULL;
 	bitmap = calloc(sizeof(csch_cbitmap_t), 1);
 
-	csch_cobj_init(&bitmap->hdr, sheet, oid, CSCH_CTYPE_BITMAP, CSCH_INVALID_OID);
+	csch_cobj_init(&bitmap->hdr, sheet, parent, oid, CSCH_CTYPE_BITMAP);
 	return bitmap;
 }
 
@@ -49,9 +49,9 @@
 	free(bitmap);
 }
 
-csch_cbitmap_t *csch_cbitmap_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_cbitmap_t *csch_cbitmap_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid)
 {
-	csch_cbitmap_t *bitmap = htip_get(&sheet->id2obj, oid);
+	csch_cbitmap_t *bitmap = htip_get(&grp->id2obj, oid);
 	if ((bitmap != NULL) && (bitmap->hdr.type != CSCH_CTYPE_BITMAP))
 		return NULL;
 	return bitmap;
Index: trunk/src/libcschem/cnc_bitmap.h
===================================================================
--- trunk/src/libcschem/cnc_bitmap.h	(revision 572)
+++ trunk/src/libcschem/cnc_bitmap.h	(revision 573)
@@ -40,6 +40,6 @@
 
 csch_cbitmap_t *csch_cbitmap_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_cbitmap_free(csch_cbitmap_t *bitmap);
-csch_cbitmap_t *csch_cbitmap_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_cbitmap_t *csch_cbitmap_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid);
 
 #endif
Index: trunk/src/libcschem/cnc_conn.c
===================================================================
--- trunk/src/libcschem/cnc_conn.c	(revision 572)
+++ trunk/src/libcschem/cnc_conn.c	(revision 573)
@@ -34,12 +34,12 @@
 {
 	csch_conn_t *conn;
 
-	conn = htip_get(&sheet->id2obj, oid);
+	conn = htip_get(&parent->id2obj, oid);
 	if (conn != NULL)
 		return NULL;
 	conn = calloc(sizeof(csch_conn_t), 1);
 
-	csch_cobj_init(&conn->hdr, sheet, oid, CSCH_CTYPE_CONN, CSCH_INVALID_OID);
+	csch_cobj_init(&conn->hdr, sheet, parent, oid, CSCH_CTYPE_CONN);
 	return conn;
 }
 
@@ -51,7 +51,7 @@
 
 csch_conn_t *csch_conn_get(csch_sheet_t *sheet, csch_oid_t oid)
 {
-	csch_conn_t *conn = htip_get(&sheet->id2obj, oid);
+	csch_conn_t *conn = htip_get(&sheet->direct.id2obj, oid);
 	if ((conn != NULL) && (conn->hdr.type != CSCH_CTYPE_CONN))
 		return NULL;
 	return conn;
Index: trunk/src/libcschem/cnc_grp.c
===================================================================
--- trunk/src/libcschem/cnc_grp.c	(revision 572)
+++ trunk/src/libcschem/cnc_grp.c	(revision 573)
@@ -30,17 +30,24 @@
 #include "cnc_grp.h"
 #include "cnc_obj.h"
 
+csch_cgrp_t *csch_cgrp_init(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_cgrp_t *parent, csch_oid_t oid)
+{
+	csch_cobj_init(&grp->hdr, sheet, parent, oid, CSCH_CTYPE_GRP);
+	htip_init(&grp->id2obj, longhash, longkeyeq);
+	return grp;
+}
+
+
 csch_cgrp_t *csch_cgrp_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid)
 {
 	csch_cgrp_t *grp;
 
-	grp = htip_get(&sheet->id2obj, oid);
+	grp = htip_get(&parent->id2obj, oid);
 	if (grp != NULL)
 		return NULL;
 	grp = calloc(sizeof(csch_cgrp_t), 1);
 
-	csch_cobj_init(&grp->hdr, sheet, oid, CSCH_CTYPE_GRP, CSCH_INVALID_OID);
-	return grp;
+	return csch_cgrp_init(sheet, grp, parent, oid);
 }
 
 void csch_cgrp_free(csch_cgrp_t *grp)
@@ -49,9 +56,9 @@
 	free(grp);
 }
 
-csch_cgrp_t *csch_cgrp_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_cgrp_t *csch_cgrp_get(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid)
 {
-	csch_cgrp_t *grp = htip_get(&sheet->id2obj, oid);
+	csch_cgrp_t *grp = htip_get(&parent->id2obj, oid);
 	if ((grp != NULL) && (grp->hdr.type != CSCH_CTYPE_GRP))
 		return NULL;
 	return grp;
@@ -64,12 +71,12 @@
 {
 	csch_cgrp_ref_t *grp;
 
-	grp = htip_get(&sheet->id2obj, oid);
+	grp = htip_get(&parent->id2obj, oid);
 	if (grp != NULL)
 		return NULL;
 	grp = calloc(sizeof(csch_cgrp_ref_t), 1);
 
-	csch_cobj_init(&grp->hdr, sheet, oid, CSCH_CTYPE_GRP, CSCH_INVALID_OID);
+	csch_cobj_init(&grp->hdr, sheet, parent, oid, CSCH_CTYPE_GRP);
 	return grp;
 }
 
@@ -79,9 +86,9 @@
 	free(grp);
 }
 
-csch_cgrp_ref_t *csch_cgrp_refget(csch_sheet_t *sheet, csch_oid_t oid)
+csch_cgrp_ref_t *csch_cgrp_refget(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid)
 {
-	csch_cgrp_ref_t *grp = htip_get(&sheet->id2obj, oid);
+	csch_cgrp_ref_t *grp = htip_get(&parent->id2obj, oid);
 	if ((grp != NULL) && (grp->hdr.type != CSCH_CTYPE_GRP))
 		return NULL;
 	return grp;
Index: trunk/src/libcschem/cnc_grp.h
===================================================================
--- trunk/src/libcschem/cnc_grp.h	(revision 572)
+++ trunk/src/libcschem/cnc_grp.h	(revision 573)
@@ -42,13 +42,13 @@
 
 csch_cgrp_t *csch_cgrp_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_cgrp_free(csch_cgrp_t *grp);
-csch_cgrp_t *csch_cgrp_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_cgrp_t *csch_cgrp_get(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 
 /*** standard calls on group refs ***/
 
 csch_cgrp_ref_t *csch_cgrp_ref_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_cgrp_ref_free(csch_cgrp_ref_t *grp);
-csch_cgrp_ref_t *csch_cgrp_ref_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_cgrp_ref_t *csch_cgrp_ref_get(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 
 /*** non-standard calls on groups ***/
 void csch_cgrp_insert_(csch_cgrp_t *grp, csch_chdr_t *hdr);
Index: trunk/src/libcschem/cnc_line.c
===================================================================
--- trunk/src/libcschem/cnc_line.c	(revision 572)
+++ trunk/src/libcschem/cnc_line.c	(revision 573)
@@ -35,12 +35,12 @@
 {
 	csch_line_t *line;
 
-	line = htip_get(&sheet->id2obj, oid);
+	line = htip_get(&parent->id2obj, oid);
 	if (line != NULL)
 		return NULL;
 	line = calloc(sizeof(csch_line_t), 1);
 
-	csch_cobj_init(&line->hdr, sheet, oid, CSCH_CTYPE_LINE, CSCH_INVALID_OID);
+	csch_cobj_init(&line->hdr, sheet, parent, oid, CSCH_CTYPE_LINE);
 	return line;
 }
 
@@ -50,9 +50,9 @@
 	free(line);
 }
 
-csch_line_t *csch_line_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_line_t *csch_line_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid)
 {
-	csch_line_t *line = htip_get(&sheet->id2obj, oid);
+	csch_line_t *line = htip_get(&grp->id2obj, oid);
 	if ((line != NULL) && (line->hdr.type != CSCH_CTYPE_LINE))
 		return NULL;
 	return line;
Index: trunk/src/libcschem/cnc_line.h
===================================================================
--- trunk/src/libcschem/cnc_line.h	(revision 572)
+++ trunk/src/libcschem/cnc_line.h	(revision 573)
@@ -40,7 +40,7 @@
 
 csch_line_t *csch_line_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_line_free(csch_line_t *line);
-csch_line_t *csch_line_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_line_t *csch_line_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid);
 void csch_line_update(csch_line_t *line);
 
 #endif
Index: trunk/src/libcschem/cnc_loop.h
===================================================================
--- trunk/src/libcschem/cnc_loop.h	(revision 572)
+++ trunk/src/libcschem/cnc_loop.h	(revision 573)
@@ -29,56 +29,58 @@
 /*** API ***/
 
 /* Iterate over sheet objects */
-typedef struct csch_sheeto_iter_s csch_sheeto_iter_t;
-csch_inline csch_chdr_t *csch_sheeto_first(csch_sheeto_iter_t *it, const csch_sheet_t *sheet);
-csch_inline csch_chdr_t *csch_sheeto_next(csch_sheeto_iter_t *it);
+typedef struct csch_grpo_iter_s csch_grpo_iter_t;
+csch_inline csch_chdr_t *csch_grpo_first(csch_grpo_iter_t *it, const csch_sheet_t *sheet, const csch_cgrp_t *grp);
+csch_inline csch_chdr_t *csch_grpo_next(csch_grpo_iter_t *it);
 
 /* this one also includes removed objects in the iteration */
-csch_inline csch_chdr_t *csch_sheeto_first_with_rem(csch_sheeto_iter_t *it, const csch_sheet_t *sheet);
+csch_inline csch_chdr_t *csch_grpo_first_with_rem(csch_grpo_iter_t *it, const csch_sheet_t *sheet, const csch_cgrp_t *grp);
 
 
 
 /*** Implementation ***/
 
-struct csch_sheeto_iter_s {
+struct csch_grpo_iter_s {
 	unsigned removed:1;
 	const csch_sheet_t *sheet;
+	const csch_cgrp_t *grp;
 	htip_entry_t *e;
 };
 
-csch_inline csch_chdr_t *csch_sheeto_first_(csch_sheeto_iter_t *it, const csch_sheet_t *sheet)
+csch_inline csch_chdr_t *csch_grpo_first_(csch_grpo_iter_t *it, const csch_sheet_t *sheet, const csch_cgrp_t *grp)
 {
 	csch_chdr_t *h;
 
 	it->sheet = sheet;
-	it->e = htip_first(&it->sheet->id2obj);
+	it->grp = grp;
+	it->e = htip_first(&it->grp->id2obj);
 	if (it->e == NULL)
 		return NULL;
 
 	h = it->e->value;
 	if ((!it->removed) && (h->removed))
-		return csch_sheeto_next(it);
+		return csch_grpo_next(it);
 
 	return h;
 }
 
-csch_inline csch_chdr_t *csch_sheeto_first(csch_sheeto_iter_t *it, const csch_sheet_t *sheet)
+csch_inline csch_chdr_t *csch_grpo_first(csch_grpo_iter_t *it, const csch_sheet_t *sheet, const csch_cgrp_t *grp)
 {
 	it->removed = 0;
-	return csch_sheeto_first_(it, sheet);
+	return csch_grpo_first_(it, sheet, grp);
 }
 
-csch_inline csch_chdr_t *csch_sheeto_first_with_rem(csch_sheeto_iter_t *it, const csch_sheet_t *sheet)
+csch_inline csch_chdr_t *csch_grpo_first_with_rem(csch_grpo_iter_t *it, const csch_sheet_t *sheet, const csch_cgrp_t *grp)
 {
 	it->removed = 1;
-	return csch_sheeto_first_(it, sheet);
+	return csch_grpo_first_(it, sheet, grp);
 }
 
-csch_inline csch_chdr_t *csch_sheeto_next(csch_sheeto_iter_t *it)
+csch_inline csch_chdr_t *csch_grpo_next(csch_grpo_iter_t *it)
 {
 	for(;;) {
 		csch_chdr_t *h;
-		it->e = htip_next(&it->sheet->id2obj, it->e);
+		it->e = htip_next(&it->grp->id2obj, it->e);
 		if (it->e == NULL)
 			return NULL;
 
Index: trunk/src/libcschem/cnc_obj.h
===================================================================
--- trunk/src/libcschem/cnc_obj.h	(revision 572)
+++ trunk/src/libcschem/cnc_obj.h	(revision 573)
@@ -46,7 +46,7 @@
 /* Initialize an object by setting the common header fields; the only purpose
    of this function is to get compiler warnings at every caller when the header
    is extended (because the number of args would be extended here) */
-csch_inline void csch_cobj_init(csch_chdr_t *dst, csch_sheet_t *sheet, csch_oid_t oid, csch_ctype_t type, csch_oid_t parent)
+csch_inline void csch_cobj_init(csch_chdr_t *dst, csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid, csch_ctype_t type)
 {
 	dst->oid = oid;
 	dst->type = type;
@@ -55,8 +55,8 @@
 	dst->sheet = sheet;
 	csch_bbox_reset(&dst->bbox);
 	csch_attrib_init(&dst->attr);
-	htip_set(&sheet->id2obj, oid, dst);
-
+	if (dst->parent != NULL)
+		htip_set(&parent->id2obj, oid, dst);
 }
 
 csch_inline void csch_cobj_uninit(csch_chdr_t *dst)
@@ -64,8 +64,8 @@
 	csch_chdr_t *o;
 
 #ifndef NDEBUG
-	if (dst->sheet != NULL) {
-		o = htip_pop(&dst->sheet->id2obj, dst->oid);
+	if ((dst->sheet != NULL) && (dst->parent != NULL)) {
+		o = htip_pop(&dst->parent->id2obj, dst->oid);
 		if (o != NULL)
 			assert(o == dst);
 	}
Index: trunk/src/libcschem/cnc_pen.c
===================================================================
--- trunk/src/libcschem/cnc_pen.c	(revision 572)
+++ trunk/src/libcschem/cnc_pen.c	(revision 573)
@@ -42,12 +42,12 @@
 {
 	csch_cpen_t *pen;
 
-	pen = htip_get(&sheet->id2obj, oid);
+	pen = htip_get(&parent->id2obj, oid);
 	if (pen != NULL)
 		return NULL;
 	pen = calloc(sizeof(csch_cpen_t), 1);
 
-	csch_cobj_init(&pen->hdr, sheet, oid, CSCH_CTYPE_PEN, CSCH_INVALID_OID);
+	csch_cobj_init(&pen->hdr, sheet, parent, oid, CSCH_CTYPE_PEN);
 	return pen;
 }
 
@@ -58,7 +58,7 @@
 
 	/* remove cached pens from any object */
 	if (sheet != NULL) {
-		for(e = htip_first(&sheet->id2obj); e; e = htip_next(&sheet->id2obj, e)) {
+		for(e = htip_first(&pen->hdr.parent->id2obj); e; e = htip_next(&pen->hdr.parent->id2obj, e)) {
 			csch_chdr_t *hdr = e->value;
 			if ((hdr->pen_oid == pen->hdr.oid) || (hdr->pen == pen))
 				hdr->pen = NULL;
@@ -69,9 +69,9 @@
 }
 
 
-csch_cpen_t *csch_pen_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_cpen_t *csch_pen_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid)
 {
-	csch_cpen_t *pen = htip_get(&sheet->id2obj, oid);
+	csch_cpen_t *pen = htip_get(&grp->id2obj, oid);
 	if ((pen != NULL) && (pen->hdr.type != CSCH_CTYPE_PEN))
 		return NULL;
 	return pen;
Index: trunk/src/libcschem/cnc_pen.h
===================================================================
--- trunk/src/libcschem/cnc_pen.h	(revision 572)
+++ trunk/src/libcschem/cnc_pen.h	(revision 573)
@@ -46,7 +46,7 @@
 
 csch_cpen_t *csch_pen_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_pen_free(csch_cpen_t *pen);
-csch_cpen_t *csch_pen_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_cpen_t *csch_pen_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid);
 
 extern csch_cpen_t csch_pen_default_unknown;
 
@@ -54,9 +54,9 @@
 csch_inline csch_cpen_t *csch_pen_(csch_chdr_t *hdr)
 {
 	if (hdr->pen == NULL) {
-		csch_sheet_t *sheet = hdr->sheet;
-		if (sheet != NULL)
-			hdr->pen = csch_pen_get(sheet, hdr->pen_oid);
+		csch_cgrp_t *grp = hdr->parent;
+		if (grp != NULL)
+			hdr->pen = csch_pen_get(hdr->sheet, grp, hdr->pen_oid);
 	}
 	if (hdr->pen == NULL)
 		return &csch_pen_default_unknown;
Index: trunk/src/libcschem/cnc_poly.c
===================================================================
--- trunk/src/libcschem/cnc_poly.c	(revision 572)
+++ trunk/src/libcschem/cnc_poly.c	(revision 573)
@@ -34,12 +34,12 @@
 {
 	csch_cpoly_t *poly;
 
-	poly = htip_get(&sheet->id2obj, oid);
+	poly = htip_get(&parent->id2obj, oid);
 	if (poly != NULL)
 		return NULL;
 	poly = calloc(sizeof(csch_cpoly_t), 1);
 
-	csch_cobj_init(&poly->hdr, sheet, oid, CSCH_CTYPE_POLY, CSCH_INVALID_OID);
+	csch_cobj_init(&poly->hdr, sheet, parent, oid, CSCH_CTYPE_POLY);
 	return poly;
 }
 
@@ -49,9 +49,9 @@
 	free(poly);
 }
 
-csch_cpoly_t *csch_cpoly_get(csch_sheet_t *sheet, csch_oid_t oid)
+csch_cpoly_t *csch_cpoly_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid)
 {
-	csch_cpoly_t *poly = htip_get(&sheet->id2obj, oid);
+	csch_cpoly_t *poly = htip_get(&grp->id2obj, oid);
 	if ((poly != NULL) && (poly->hdr.type != CSCH_CTYPE_POLY))
 		return NULL;
 	return poly;
Index: trunk/src/libcschem/cnc_poly.h
===================================================================
--- trunk/src/libcschem/cnc_poly.h	(revision 572)
+++ trunk/src/libcschem/cnc_poly.h	(revision 573)
@@ -39,6 +39,6 @@
 
 csch_cpoly_t *csch_cpoly_alloc(csch_sheet_t *sheet, csch_cgrp_t *parent, csch_oid_t oid);
 void csch_cpoly_free(csch_cpoly_t *poly);
-csch_cpoly_t *csch_cpoly_get(csch_sheet_t *sheet, csch_oid_t oid);
+csch_cpoly_t *csch_cpoly_get(csch_sheet_t *sheet, csch_cgrp_t *grp, csch_oid_t oid);
 
 #endif
Index: trunk/src/libcschem/concrete.c
===================================================================
--- trunk/src/libcschem/concrete.c	(revision 572)
+++ trunk/src/libcschem/concrete.c	(revision 573)
@@ -36,11 +36,11 @@
 {
 	csch_sheet_t *sheet = calloc(sizeof(csch_sheet_t), 1);
 
-	htip_init(&sheet->id2obj, longhash, longkeyeq);
 	csch_rtree_init(&sheet->rtree);
-	csch_cobj_init(&sheet->direct.hdr, sheet, oid, CSCH_CTYPE_GRP, CSCH_INVALID_OID);
-	csch_cobj_init(&sheet->indirect.hdr, sheet, oid, CSCH_CTYPE_GRP, CSCH_INVALID_OID);
-	sheet->next_id = oid+1;
+
+	csch_cgrp_init(sheet, &sheet->direct.hdr, NULL, oid);
+	csch_cgrp_init(sheet, &sheet->indirect.hdr, NULL, oid);
+
 	csch_bbox_invalidate(&sheet->bbox);
 	return sheet;
 }
@@ -53,18 +53,17 @@
 #warning TODO: free all objects in the hash
 	csch_rtree_uninit(&sheet->rtree);
 
-	htip_uninit(&sheet->id2obj);
 	free(sheet->filename);
 	free(sheet);
 }
 
-void csch_sheet_bbox_update(csch_sheet_t *sheet)
+static void csch_sheet_bbox_update_(csch_sheet_t *sheet, csch_cgrp_t *grp)
 {
 	csch_chdr_t *h;
-	csch_sheeto_iter_t it;
+	csch_grpo_iter_t it;
 
 	csch_bbox_reset(&sheet->bbox);
-	for(h = csch_sheeto_first(&it, sheet); h != NULL; h = csch_sheeto_next(&it)) {
+	for(h = csch_grpo_first(&it, sheet, grp); h != NULL; h = csch_grpo_next(&it)) {
 		if (csch_bbox_is_invalid(&h->bbox))
 			continue;
 		csch_bbox_bump(&sheet->bbox, x, h->bbox.x1);
@@ -74,8 +73,13 @@
 	}
 }
 
-csch_oid_t csch_oid_new(csch_sheet_t *sheet)
+void csch_sheet_bbox_update(csch_sheet_t *sheet)
 {
-	assert(sheet->next_id < CSCH_MAX_OID);
-	return sheet->next_id++;
+	csch_sheet_bbox_update_(sheet, &sheet->direct);
 }
+
+csch_oid_t csch_oid_new(csch_sheet_t *sheet, csch_cgrp_t *grp)
+{
+	assert(grp->next_id < CSCH_MAX_OID);
+	return grp->next_id++;
+}
Index: trunk/src/libcschem/concrete.h
===================================================================
--- trunk/src/libcschem/concrete.h	(revision 572)
+++ trunk/src/libcschem/concrete.h	(revision 573)
@@ -37,6 +37,7 @@
 /* Forward declare basic types other objects depend on */
 typedef struct csch_pen_s csch_cpen_t;
 typedef struct csch_sheet_s csch_sheet_t;
+typedef struct csch_cgrp_s csch_cgrp_t;
 
 typedef enum csch_ctype_s {
 	CSCH_CTYPE_INVALID = 0,
@@ -53,7 +54,7 @@
 struct csch_chdr_s {
 	csch_oid_t oid;
 	csch_ctype_t type;
-	csch_oid_t parent;
+	csch_cgrp_t *parent;
 	htsp_t attr;
 	unsigned removed:1;
 	csch_oid_t pen_oid;
@@ -64,14 +65,14 @@
 	csch_rtree_box_t bbox;
 };
 
-typedef struct csch_cgrp_s { /* type=CSCH_CTYPE_GRP */
+struct csch_cgrp_s { /* type=CSCH_CTYPE_GRP */
 	csch_chdr_t hdr;
-	htip_t memb;          /* id -> object pointer (primary storage); rarely delete from this (undo needs deleted objects) */
+	htip_t id2obj;          /* members (memb): id -> object pointer (primary storage); rarely delete from this (undo needs deleted objects) */
 	csch_oid_t next_id;
 
 	double rot;
 	csch_coord_t xc, yc, x, y;
-} csch_cgrp_t;
+};
 
 struct csch_sheet_s {
 	csch_rtree_t rtree;     /* IDs in screen coords */
@@ -102,7 +103,7 @@
 csch_inline const csch_rtree_box_t *csch_sheet_bbox(csch_sheet_t *sheet);
 void csch_sheet_bbox_update(csch_sheet_t *sheet);
 
-csch_oid_t csch_oid_new(csch_sheet_t *sheet);
+csch_oid_t csch_oid_new(csch_sheet_t *sheet, csch_cgrp_t *grp);
 
 
 /*** implementation ***/
Index: trunk/src/plugins/export_animator/export_animator.c
===================================================================
--- trunk/src/plugins/export_animator/export_animator.c	(revision 572)
+++ trunk/src/plugins/export_animator/export_animator.c	(revision 573)
@@ -94,7 +94,7 @@
 {
 	FILE *f;
 	csch_chdr_t *h;
-	csch_sheeto_iter_t it;
+	csch_grpo_iter_t it;
 	ctx_t ctx;
 	const csch_rtree_box_t *shbb;
 	csch_coord_t mx, my;
@@ -115,7 +115,7 @@
 	ctx.fn = fn;
 	ctx.f = f;
 	ctx.sheet = src;
-	for(h = csch_sheeto_first(&it, src); h != NULL; h = csch_sheeto_next(&it))
+	for(h = csch_grpo_first(&it, src, &src->direct); h != NULL; h = csch_grpo_next(&it))
 		anim_draw_obj(&ctx, h);
 
 	fprintf(f, "flush\n");
Index: trunk/src/plugins/io_lihata/read.c
===================================================================
--- trunk/src/plugins/io_lihata/read.c	(revision 572)
+++ trunk/src/plugins/io_lihata/read.c	(revision 573)
@@ -83,7 +83,7 @@
 }
 
 /* Convert an oid from string, making sure there's no duplicate */
-static csch_oid_t load_oid(read_ctx_t *ctx, lht_node_t *nd, const char *oids)
+static csch_oid_t load_oid(read_ctx_t *ctx, csch_cgrp_t *parent, lht_node_t *nd, const char *oids)
 {
 	csch_oid_t oid;
 	char *end;
@@ -94,13 +94,13 @@
 		return 0;
 	}
 
-	if ((htip_get(&ctx->sheet->id2obj, oid) != NULL) || (oid == ctx->sheet->direct.hdr.oid)) {
+	if ((htip_get(&parent->id2obj, oid) != NULL) || (oid == ctx->sheet->direct.hdr.oid)) {
 		error(nd, ("duplicate oid %lu\n", oid));
 		return 0;
 	}
 
-	if (oid >= ctx->sheet->next_id)
-		ctx->sheet->next_id = oid+1;
+	if (oid >= parent->next_id)
+		parent->next_id = oid+1;
 
 	return oid;
 }
@@ -108,7 +108,7 @@
 /* Make sure node name matches the expected name and node type matches
    the expected type. On match, parse or invent the oid and return it. On
    error return 0. */
-csch_oid_t check_type_oid_(read_ctx_t *ctx, lht_node_t *nd, const char *name, int namelen, lht_node_type_t type)
+csch_oid_t check_type_oid_(read_ctx_t *ctx, csch_cgrp_t *grp, lht_node_t *nd, const char *name, int namelen, lht_node_type_t type)
 {
 	const char *oids;
 	csch_oid_t oid;
@@ -124,19 +124,21 @@
 
 	oids = nd->name + namelen;
 #warning TODO: delayed ID allocation!
-	if (*oids == '\0')
-		return ctx->sheet->next_id++;
+	if (*oids == '\0') {
+		return -1;
+/*		return ctx->sheet->next_id++;*/
+	}
 	if (*oids != '.') {
 		error(nd, ("invalid ID appendix or wrong node name (expected %s.<integer> got %s)\n", name, nd->name));
 		return 0;
 	}
 
-	return load_oid(ctx, nd, oids+1);
+	return load_oid(ctx, grp, nd, oids+1);
 }
 
 /* shorthand with compile-time string length */
-#define check_type_oid(ctx, nd, name, type) \
-	check_type_oid_(ctx, nd, #name, strlen(#name), type)
+#define check_type_oid(ctx, grp, nd, name, type) \
+	check_type_oid_(ctx, grp, nd, #name, strlen(#name), type)
 
 #warning TODO: revise whether this is needed at all
 #if 0
@@ -184,7 +186,7 @@
 
 	if (sep != NULL) {
 		len = sep - nd->name;
-		oid = load_oid(ctx, nd, sep+1);
+		oid = load_oid(ctx, parent, nd, sep+1);
 		if (oid == 0)
 			return -1;
 	}
@@ -338,7 +340,7 @@
 }
 
 
-static int parse_pens(read_ctx_t *ctx, lht_node_t *subtree)
+static int parse_pens(read_ctx_t *ctx, csch_cgrp_t *grp, lht_node_t *subtree)
 {
 	lht_node_t *ndpen;
 	lht_dom_iterator_t it;
@@ -352,7 +354,7 @@
 	}
 
 	for(ndpen = lht_dom_first(&it, subtree); ndpen != NULL; ndpen = lht_dom_next(&it)) {
-		csch_oid_t oid = check_type_oid(ctx, ndpen, pen, LHT_HASH);
+		csch_oid_t oid = check_type_oid(ctx, grp, ndpen, pen, LHT_HASH);
 		csch_cpen_t *pen;
 		if (oid == 0)
 			return -1;
@@ -481,6 +483,7 @@
 	}
 
 	parent = direct ? &ctx->sheet->direct : &ctx->sheet->indirect;
+
 	return dispatch_subtree(ctx, parent, subtree, objs_tbl, 1);
 }
 
@@ -493,8 +496,10 @@
 /*	parse_uid(&ctx->sheet->uid, lht_dom_hash_get(subtree, "uid"));*/
 	if (parse_attribs(ctx, &ctx->sheet->direct.hdr.attr, lht_dom_hash_get(subtree, "attrib")) != 0)
 		return -1;
-	if (parse_pens(ctx, lht_dom_hash_get(subtree, "pens")) != 0)
+
+	if (parse_pens(ctx, &ctx->sheet->direct, lht_dom_hash_get(subtree, "pens")) != 0)
 		return -1;
+
 	if (parse_sheet_objs(ctx, lht_dom_hash_get(subtree, "obj_indirect"), 0) != 0)
 		return -1;
 	if (parse_sheet_objs(ctx, lht_dom_hash_get(subtree, "obj_direct"), 1) != 0)