About
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Duck_Tree is kinda-sorta a MPTT/NestedSet implementation for Zend_Db_Table. It
mostly uses MPTT but in a few places it falls back on an adjacency list style
lookups for simplicity or speed. It's also not exactly a tree structure because
it allows multiple root nodes but I believe this to be a feature, and not a bug.

Regardless of the specifics, I wrote it because I couldn't find a full-featured
MPTT library for Zend_Db_Table. That was a year ago, and I'm a little fuzzy on
this code now, but I've cleaned it up a bit and putting it out there. I hope it
proves useful.

Important notes
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- Your table must have a single primary key.
- The code assumes the following fields exist: lft, rgt, parent_id
- The test suite included is from an older version of the library and is, in
  honesty, not very good. I need to find the newer version and post it.

Thanks to:
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- Warnar Boekkooi who added the move function and several improvements.
- DMM Websolutions and InGoedeBanen who sponsored additional development.
- I remember reading the django-treebeard code when I wrote this. So them too.