Do we need Tag and Peer when reading NDEF messages?

For incoming messages, do we care if the message came from a peer or a tag?
The current Windows and BlackBerry webworks API just give you an NDEF
message, they don't indicate a source.

Since we're only covering NDEF, the tag is almost irrelevant, unless we
want to allow implementers to be able to add tag meta data (id, nfc forum
tag type, technology, size, locked/unlocked, writable).

Incoming messages could be handled by nfc.onmessage. This could make
reading messages much simpler.