XForms 2.0 spec review: External JSON values

All,

Some comments about the JSON support:

1. "This format can be serialized back to JSON with a submission
element with a serialization attribute value of "application/json"."

Q1. We need to specify what happens if the format is invalid during submission.
Q2. Related: should we explicitly say that unknown elements/attributes
are ignored? Or only those in a namespace? This could be useful so
that you can locally annotate the XML document yet still submit it
back to JSON.

2. "marked by the header parameter of the media type"

Q3. How is this specified in the mediatype?

Comments welcome.

-Erik