project, and with assistance from Oleg Broytmann.  Specifically,

get_param(), get_params(): Document that these methods may return
parameter values that are either strings, or 3-tuples in the case of
RFC 2231 encoded parameters.  The application should be prepared to
deal with such return values.

get_boundary(): Be prepared to deal with RFC 2231 encoded boundary
parameters.  It makes little sense to have boundaries that are
anything but ascii, so if we get back a 3-tuple from get_param() we
will decode it into ascii and let any failures percolate up.

get_content_charset(): New method which treats the charset parameter
just like the boundary parameter in get_boundary().  Note that
"get_charset()" was already taken to return the default Charset
object.

get_charsets(): Rewrite to use get_content_charset().