PHP libraries for handling nested sets in MySQL

I read this article Managing Hierarchical Data in MySQL

At the end of this article, it writes about PHP libraries for ha开发者_如何学Gondling nested sets in MySQL.

Does anyone know which PHP libraries he is talking about?

Propel 1.3/1.4 have very nice nested set support: http://propel.phpdb.org/trac/wiki/Users/Documentation/1.3/Tree/NestedSet