- ``datrie`` can be used to improve parsing performance (though in

almost all cases the improvement is trivial);

- ``lxml`` is supported as a tree format (for both building and

walking) under CPython (but *not* PyPy where it is known to cause

segfaults);

- ``genshi`` has a treewalker (but not builder); and

- ``chardet`` (note currently this is only packaged on PyPi for

Python 2, though several package managers include unofficial ports

to Python 3) can be used as a fallback when character encoding

cannot be determined.

- We aim to follow PEP 8 in the library, but ignoring the

79-character-per-line limit, instead following a soft limit of 99,

but allowing lines over this where it is the readable thing to do.

- We keep pyflakes reporting no errors or warnings at all times.

- We keep the master branch passing all tests at all times on all

supported versions.