What I have in mind for content integrity is twofold. One is
something like "this MIME message part is delivered intact".
Another is more complicated, which is something like,
"it displays properly (as the designer intended; except for
framing; ...)". Hard questions, but I think we can make
progress on them in a practical sense; in a formal sense,
I agreewe that they are hard.
Wrt to non-delivery, separating it semantically from "modification"
is an important simplication. To a large degree, web access is
controlled by policy that blocks specific content. In other
cases, requests might not be satisfied because resources
aren't available in a timely manner. These things have
analogs at the IP network layer, and they are not considered
modification. My original message noted that integrity
is different from reliability.
How is content integrity defined? Is this the default behavior where no
actions/services on the content are performed by the box? If an action
is performed, how will we validate integrity?
Refusal to deliver content is not modification
Is this policy based or are there other reasons for the OPES box to
deny delivery of content?