BACKWARDS COMPATIBILITY GUIDELINES
These guidelines have been adopted by the P3P
Specification Working Group Meeting of 7 May 2003
The (draft) P3P 1.1 working group charter states "The P3P 1.1
Specification should be designed for backwards compatibility with the P3P 1.0
Specification." Here are some details of what this means and how we will
apply this as the working group goes about its business. This is not intended
to be a comprehensive or absolute set of requirements, but rather a set of
guidelines to help the group work towards a common goal. Working group
members should keep these guidelines in mind when making proposals to the
working group and avoid proposals inconsistent with these guidelines.
- P3P 1.0 user agents should be able to process P3P 1.1 policies and
policy reference files. This implies both that the P3P 1.1 policies and
policy reference files are fully compliant with the P3P 1.0 XML schema,
and that the semantics of these files will not be misinterpreted by a
user agent that interprets them according to the P3P 1.0
- New vocabulary elements and syntax introduced in P3P 1.1 should be
introduced as optional extensions using the P3P 1.0 extension
- New or changed P3P HTTP headers that are not backwards-compatible with
P3P 1.0 should use a new prefix to differentiate them from those used in
P3P 1.0. They should be designed such that sites that wish to make their
P3P headers accessible to both P3P 1.0 and P3P 1.1 user agents can
include both the P3P 1.0 and P3P 1.1 headers.
- Changes to requirements or definitions introduced in P3P 1.1. should
add clarity where the P3P 1.0 specification is ambiguous, but should not
cause a particular P3P vocabulary element to have different meanings in
P3P 1.0 and P3P 1.1.
- New requirements or features may be introduced in the P3P 1.1
specification if they do not impact the ability of P3P 1.0 user agents to
process P3P 1.1 policies and policy reference files. For example, a
feature that would enable P3P policies to be referenced from arbitrary
XML documents would not impact P3P 1.0 user agents, since those user
agents do not attempt to find P3P policy references in arbitrary XML
documents. Of course, P3P 1.0 user agents are not expected to comply with
new requirements introduced in P3P 1.1.
- Features, vocabulary elements, or requirements may be removed in the
P3P 1.1 specification as long as they do not cause a P3P 1.0 user agent
to be unable to process a P3P 1.1 policy or policy reference file.