Tips/tricks/hints for writing new fixers:

    * Don't write your own PATTERN from scratch; that's what
      scripts/find_pattern.py is for.
    
    * If your fixer works by changing a node's children list or a leaf's value,
      be sure to call the node/leaf's changed() method. This to be sure the main
      script will recognize that the tree has changed.


Putting 2to3 to work somewhere else:

    * By default, 2to3 uses a merger of Python 2.x and Python 3's grammars.  If
      you want to support a different grammar, just replace the Grammar.txt file
      with Grammar/Grammar from your chosen Python version.

    * The real heart of 2to3 is the concrete syntax tree parser in pgen2; this
      chunk of the system is suitable for a wide range of applications that
      require CST transformation. All that's required is to rip off the fixer
      layer and replace it with something else that walks the tree. One
      application would be a tool to check/enforce style guidelines; this could
      leverage 90% of the existing infrastructure with primarily cosmetic
      changes (e.g., fixes/fix_*.py -> styles/style_*.py).


TODO

    Simple:
    #######
    
    * Refactor common code out of fixes/fix_*.py into fixer_util (on-going).

    * Document how to write fixers.


    Complex:
    ########

    * Come up with a scheme to hide the details of suite indentation (some kind
      of custom pytree node for suites, probably). This will automatically
      reindent all code with spaces, tied into a refactor.py flag that allows
      you to specify the indent level.

    * Remove the need to explicitly assign a node's parent attribute.  This
      could be gone with a magic children list.

    * Import statements are complicated and a pain to handle, and there are many
      fixers that manipulate them. It would be nice to have a little API for
      manipulating imports in fixers.