I don't know enough about PEM to know the right way to do this. Can all
the necessary information be fit into the content-type, version-number,
and resource-reference? If so, all we need is some clear prose
explaining it. As with compression, I'm not the right person to do
this, but I think that a PEM-message content-type is quite possibly a
reasonable thing to define.
Bear in mind, also, that people can define additional content-types
after this RFC is finished. The list in this RFC is intended to provide
us with a good shared starting point, but it is not intended to preclude
future content-type definitions. -- Nathaniel