code: function _foldable_p(node){
  	var ret = false;
  	// console.log("  " + dd(node.id()));
  	if( anchor.is_root_node(node.id()) &&
  	    ! node.subgraph() && // cannot fold if already folded into
  	    anchor.get_child_nodes(node.id()).length === 1 ){
  		// console.log("    Y root_p: " +
  		// 	    anchor.is_root_node(node.id()) +
  		// 	    ";  kids: " +
  		// 	    anchor.get_child_nodes(node.id()).length);
  		ret = true;
  	    }else{
  		// console.log("    N root_p: " +
  		// 	    anchor.is_root_node(node.id()) +
  		// 	    ";  kids: " +
  		// 	    anchor.get_child_nodes(node.id()).length);
  	    }
  	return ret;
      }
docs: It is foldable if it is a root node (re: opposite of leaf--only target) and if it only has the one child (no way out--re: collapsible ).