jQuery: find a last child that has specific class

If I have deep nested unordered list and I have a reference to the root node, is there a built in way to find a last child of "li" type that has specific css class? For example if I have a tree view branch 5 levels deep, and branch is expanded down to 开发者_StackOverflow社区thrid level, levels 1,2,3 will have a class "collapsable". Now I want to find a last "li" in this case on level 3 that has this class.

Not too hard:

$("li.someclass", rootOfList).last()

searches rootOfList for the last li with class someclass