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+What
+====
+
+
+
+Syntax
+------
+
+* Lambdas and ternaries should be parsed but are not implemented (in
+  the evaluator)
+* Only floats are implemented, ``int`` literals are parsed as floats.
+* Octal and hexadecimal literals are not implemented
+* Srings are backed by JavaScript strings and probably behave like
+  ``unicode`` more than like ``str``
+* Slices don't work
+
+Builtins
+--------
+
+``py.js`` currently implements the following builtins:
+
+``type``
+    Restricted to creating new types, can't be used to get an object's
+    type (yet)
+
+``None``
+
+``True``
+
+``False``
+
+``NotImplemented``
+    Returned from rich comparison methods when the comparison is not
+    implemented for this combination of operands. In ``py.js``, this
+    is also the default implementation for all rich comparison methods.
+
+``issubclass``
+
+``object``
+
+``bool``
+    Does not inherit from ``int``, since ``int`` is not currently
+    implemented.
+
+``float``
+
+``str``
+
+``tuple``
+    Constructor/coercer is not implemented, only handles literals
+
+``list``
+    Same as tuple (``list`` is currently an alias for ``tuple``)
+
+``dict``
+    Implements trivial getting, setting and len, nothing beyond that.
+
+Note that most methods are probably missing from all of these.
+
+Data model protocols
+--------------------
+
+``py.js`` currently implements the following protocols (or
+sub-protocols) of the `Python 2.7 data model
+<>`_:
+
+Rich comparisons
+    Pretty much complete (including operator fallbacks), although the
+    behavior is currently undefined if an operation does not return
+    either a ``py.bool`` or ``NotImplemented``.
+
+    ``__hash__`` is supported (and used), but it should return **a
+    javascript string**. ``py.js``'s dict build on javascript objects,
+    reimplementing numeral hashing is worthless complexity at this
+    point.
+
+Boolean conversion
+    Implementing ``__nonzero__`` should work.
+
+Customizing attribute access
+    Protocols for getting and setting attributes (including new-style
+    extension) fully implemented but for ``__delattr__`` (since
+    ``del`` is a statement)
+
+Descriptor protocol
+    As with attributes, ``__delete__`` is not implemented.
+
+Callable objects
+    Work, although the handling of arguments isn't exactly nailed
+    down. For now, callables get two (javascript) arguments ``args``
+    and ``kwargs``, holding (respectively) positional and keyword
+    arguments.
+
+    Conflicts are *not* handled at this point.
+
+Collections Abstract Base Classes
+    Container is the only implemented ABC protocol (ABCs themselves
+    are not currently implemented) (well technically Callable and
+    Hashable are kind-of implemented as well)
+
+Numeric type emulation
+    Operators are implemented (but not tested), ``abs``, ``divmod``
+    and ``pow`` builtins are not implemented yet. Neither are ``oct``
+    and ``hex`` but I'm not sure we care (I'm not sure we care about
+    ``pow`` or even ``divmod`` either, for that matter)
+
+Utilities
+---------
+
+``py.js`` also provides (and exposes) a few utilities for "userland"
+implementation:
+
+``def``
+    Wraps a native javascript function into a ``py.js`` function, so
+    that it can be called from native expressions.
+
+    Does not ensure the return types are type-compatible with
+    ``py.js`` types.
+
+    When accessing instance methods, ``py.js`` automatically wraps
+    these in a variant of ``py.def``, to behave as Python's (bound)
+    methods.
+
+Why
+===
+
+Originally, to learn about Pratt parsers (which are very, very good at
+parsing expressions with lots of infix or mixfix symbols). The
+evaluator part came because "why not" and because I work on a product
+with the "feature" of transmitting Python expressions (over the wire)
+which the client is supposed to evaluate.
+
+How
+===
+
+At this point, only three steps exist in ``py.js``: tokenizing,
+parsing and evaluation. It is possible that a compilation step be
+added later (for performance reasons).
+
+To evaluate a Python expression, the caller merely needs to call
+`py.eval`_. `py.eval`_ takes a mandatory Python
+expression to evaluate (as a string) and an optional context, for the
+substitution of the free variables in the expression::
+
+    > py.eval("type in ('a', 'b', 'c') and foo", {type: 'c', foo: true});
+    true
+
+This is great for one-shot evaluation of expressions. If the
+expression will need to be repeatedly evaluated with the same
+parameters, the various parsing and evaluation steps can be performed
+separately: `py.eval`_ is really a shortcut for sequentially calling
+`py.tokenize`_, `py.parse`_ and `py.evaluate`_.
+
+API
+===
+
+.. _py.eval:
+
+``py.eval(expr[, context])``
+    "Do everything" function, to use for one-shot evaluation of a
+    Python expression: it will internally handle the tokenizing,
+    parsing and actual evaluation of the Python expression without
+    having to perform these separately.
+
+    ``expr``
+        Python expression to evaluate
+    ``context``
+        context dictionary holding the substitutions for the free
+        variables in the expression
+
+.. _py.tokenize:
+
+``py.tokenize(expr)``
+    ``expr``
+        Python expression to tokenize
+
+.. _py.parse:
+
+``py.parse(tokens)``
+    Parses a token stream and returns an abstract syntax tree of the
+    expression (if the token stream represents a valid Python
+    expression).
+
+    A parse tree is stateless and can be memoized and used multiple
+    times in separate evaluations.
+
+    ``tokens``
+         stream of tokens returned by `py.tokenize`_
+
+.. _py.evaluate:
+
+``py.evaluate(ast[, context])``
+    ``ast``
+        The output of `py.parse`_
+    ``context``
+        The evaluation context for the Python expression.