code: function () {
  
      	    var phynode_id = this.id;
  
  	    // Darken boxes and update current position before dragging.
      	    var assoc_phynodes = get_descendant_phynodes(phynode_id);
      	    for( var si = 0; si < assoc_phynodes.length; si++ ){
  		var phynode = assoc_phynodes[si];
  		phynode.update_position();
  		phynode.update("dim");
      	    }
  
  	    // "Dim" edges.
  	    var subtree_edges = get_descendant_connections(phynode_id);
  	    for( var se = 0; se < subtree_edges.length; se++ ){
  		var ste = subtree_edges[se];
  		ste.update("dim");
  	    }
  	}
docs: / / Phynode manipulation function definitions. / Dragging animation (color dimming).