@JorgeStolfi @jupiter_rowland @valhalla @jakob @cstross I'm not an implementer, but it's my understanding that the recipient can tell the sender what it can handle, while the sender may include a source attribute containing the original content, as well as the transformed content that complies with the recipient's stated requirements.

I think somebody above referred to the notion of degrading gracefully, and that's certainly possible using such mechanisms.