A formatter which does nothing. If writer is omitted, a
NullWriter instance is created. No methods of the writer are
called by NullFormatter instances. Implementations should
inherit from this class if implementing a writer interface but don't
need to inherit any implementation.
The standard formatter. This implementation has demonstrated wide
applicability to many writers, and may be used directly in most
circumstances. It has been used to implement a full-featured
World Wide Web browser.