When writing a custom directive based on BaseAdmonition I had to build a path of all parent sections to the current position in the document tree. I implemented this as a bottom up search starting from my custom directive using node's parent attributes. This worked fine until I put the custom directive inside an unodered list item in my reStructuredText document. I noticed list_item's backwards pointer is not set, i.e. its parent attribute is None. I would have expected list_item.parent is a reference to the corresponding bullet_list or at least some other parent element but definitely not None.
both from Debian GNU/Linux Wheezy (Testing) repositories