docs: function dblclick_event_handler(event){
  
  	    var phynode_id = this.id;
  
  	    // If this is the first double click here...
  	    var pn = get_pnode_from_phynode_id(phynode_id);
  	    if( pn.open == true ){
  		
  		// "Vanish" edges.
  		var subtree_edges = get_descendant_connections(phynode_id);
  		for( var se = 0; se < subtree_edges.length; se++ ){
  		    var ste = subtree_edges[se];
  		    ste.visible = false;
  		    ste.update();
  		}
  
  		// "Vanish" nodes and text; not this node though...
  		var subtree_nodes = get_descendant_phynodes(phynode_id);
  		for( var sn = 0; sn < subtree_nodes.length; sn++ ){
  		    var stn = subtree_nodes[sn];
  		    if( stn.id != phynode_id ){
  			// Turn of visibilty for children.
  			stn.visible = false;
  		    }else{
  			// Mark self as closed.
  			stn.open = false;
  		    }
  		    stn.update();
  		}
  	    }else{ //Otherwise...
  		
  		// Reestablish edges.
  		var subtree_edges = get_descendant_connections(phynode_id);
  		for( var se = 0; se < subtree_edges.length; se++ ){
  		    var ste = subtree_edges[se];
  		    ste.visible = true;
  		    ste.update();
  		}
  
  		// Restablish pnodes; clear all history.
  		var subtree_nodes = get_descendant_phynodes(phynode_id);
  		for( var sn = 0; sn < subtree_nodes.length; sn++ ){
  		    var stn = subtree_nodes[sn];
  		    stn.open = true;
  		    stn.visible = true;
  		    stn.update();
  		}
  	    }
  	}