Index: layer.h
===================================================================
--- layer.h	(revision 19102)
+++ layer.h	(revision 19103)
@@ -115,6 +115,8 @@
 	const char *name;              /* layer name */
 
 	pcb_layer_combining_t comb;    /* how to combine this layer with other layers in the group */
+	char *purpose;                 /* what a doc/mech layer is used for */
+	int purpi;                     /* integer version of purpose from the funtion hash (cache) */
 
 	/* for bound layers these point to the board layer's*/
 	pcb_rtree_t *line_tree, *text_tree, *polygon_tree, *arc_tree;
@@ -268,7 +270,12 @@
 int pcb_layer_rename_(pcb_layer_t *Layer, char *Name);
 int pcb_layer_recolor_(pcb_layer_t *Layer, char *color);
 
+/* Change the purpose field and recalc purpi (not undoable) */
+int pcb_layer_set_purpose__(pcb_layer_t *ly, char *purpose); /* no strdup, no event */
+int pcb_layer_set_purpose_(pcb_layer_t *ly, char *purpose); /* no strdup, send layer change event */
+int pcb_layer_set_purpose(pcb_layer_t *ly, const char *purpose); /* strdup, send event */
 
+
 /* index is 0..PCB_MAX_LAYER-1.  If old_index is -1, a new layer is
    inserted at that index.  If new_index is -1, the specified layer is
    deleted.  Returns non-zero on error, zero if OK.  */