Register the factory function with the name name. The
factory function should return an object which implements the
DOMImplementation interface. The factory function can return
the same object every time, or a new one for each call, as appropriate
for the specific implementation (e.g. if that implementation supports
some customization).
Return a suitable DOM implementation. The name is either
well-known, the module name of a DOM implementation, or
None. If it is not None, imports the corresponding module and
returns a DOMImplementation object if the import succeeds. If
no name is given, and if the environment variable PYTHON_DOM is
set, this variable is used to find the implementation.
If name is not given, consider the available implementations to find
one with the required feature set. If no implementation can be found,
raise an ImportError. The features list must be a sequence of
(feature, version) pairs which are passed to hasFeature.
In addition, xml.dom contains the Node, and the DOM
exceptions.