Limitations
***********

Things That Work
----------------

* Class constants corresponding to string enumeration constraints

* Simple and complex type definitions

* List and union datatypes

* Constraints on (simple) datatypes (e.g., minInclusive, length)

* Model groups and attribute groups

* Complex content models (all, sequence, choice); minOccurs and maxOccurs

* Abstract types, `xsi:type <http://www.w3.org/TR/xmlschema-1/#xsi_type>`_,
  substitution groups

* Nillable elements with `xsi:nil <http://www.w3.org/TR/xmlschema-1/#xsi_nil>`_

* Namespace qualified attributes and elements

* Documentation annotations present in the schema are converted to Python
  docstrings in the generated bindings.

* Pattern constraints (as long as the simple type derives from something
  that is represented as a Python string)


Things That Don't Work
----------------------

...but could someday
^^^^^^^^^^^^^^^^^^^^

* Identity constraints ("key", "unique", "keyref") are stored in the content
  model, but are not used.

* `Wildcard elements <http://www.w3.org/TR/xmlschema-1/#Wildcards>`_ are
  supported in the sense that classes that enable them in the content model
  provide access to unrecognized values through the
  :py:obj:`pyxb.binding.basis.complexTypeDefinition.wildcardElements` method.
  Where the type of the node is recognized, it is converted to a Python
  binding instance; otherwise, the xml DOM instance is stored.  Although
  namespace constraints are applied when checking for wildcard matches, the
  process contents attribute of the wildcard is ignored.

* `Wildcard attributes
  <http://www.w3.org/TR/xmlschema-1/#ag-attribute_wildcard>`_ are supported
  in much the same sense as wildcard elements: no constraints are checked,
  and all are aggregated into the
  :py:obj:`pyxb.binding.basis.complexTypeDefinition.wildcardAttributeMap`.
  Values are uninterpreted Unicode strings.

...and probably never will
^^^^^^^^^^^^^^^^^^^^^^^^^^

* The `redefine directive <http://www.w3.org/TR/xmlschema-1/#modify-schema>`_
  is not supported.

* The ability to use templates to customize binding generation was promised
  in the vision document, but after three years of no plausible use case it
  is no longer part of the plan.


Things That Mostly Work, But They're Ugly
-----------------------------------------

* The `duration <http://www.w3.org/TR/xmlschema-2/#duration>`_ type is based
  on the Python ``datetime.timedelta`` class, which works reasonably well
  for small deltas but does not handle month and year deltas.  The PyXB
  version records that information, but the ``timedelta`` functionality
  (adding/substracting from ``datetime`` instances) does not incorporate
  that portion of the delta.  Negative durations also may not work properly.
