Python 3.2 supports ElementPath version 1.3. The relevant documentation is
http://effbot.org/zone/element-xpath.htm. It says:
..	(New in 1.3) Selects the parent element.

However, a CHANGES document says:
The engine also provides limited support for the ".." parent operator; you can use it inside the subtree, but it cannot go above the target element (the element you called "find" on).  

The normal documentation should document the limitation.