code: function _reverse_foldable_p(node){
  	var ret = false;
  	if( anchor.is_leaf_node(node.id()) &&
  	    ! node.subgraph() && // cannot fold if already folded into
  	    anchor.get_parent_nodes(node.id()).length === 1 ){
  		//console.log("is foldable: " + node.id());
  		ret = true;
  	    }else{
  		//console.log("not foldable: " + node.id());
  	    }
  	// console.log("  leaf_p: " + anchor.is_leaf_node(node.id()) +
  	// 	    ";  parents: " + anchor.get_parent_nodes(node.id()).length);
  	return ret;
      }
docs: It is reverse foldable if it is a leaf node (re: opposite of root--only source) and if it only has the one child (no way out--re: collapsible ).