Duplicated guidelines for Web Content Transformation Proxies

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Duplicated guidelines for Web Content Transformation Proxies

Francois Daoust

While re-reading the spec in preparation for the F2F with a "let's think
about tests" hat, I realized that a few normative guidelines appear
duplicated. The statements already reference the other section where
they are repeated, but I think using normative terms more than once
should be avoided as it's source of confusion for implementers.

Duplicate guideline in 4.1.5 and
In 4.1.5 [1], the normative statement:
[[ It must be possible for the server to reconstruct the original User
Agent originated header fields by copying directly from the
corresponding X-Device header field values (see Original Header
Fields). ]]

... refers to [2] where it is more properly defined:
[[ When forwarding an HTTP request with altered HTTP header fields, in
addition to complying with the rules of normal HTTP operation, proxies
must include in the request copies of the unaltered header field values
in the form "X-Device-"<original header name>. ]]

 From a normative point of view, the first statement does not add
anything. I understand it is there for emphasis, but could perhaps be
turned into an informative statement that delegates to

Duplicate guideline in 4.1.6 and
In 4.1.6 [3], the normative bullet point:
[[ proxies must include a Via HTTP header field (see Proxy
Treatment of Via Header Field). ]]

... refers to [4] where the beginning of the sentence is
basically the same thing:
[[ Proxies must (in accordance with RFC 2616) include a Via HTTP header
field indicating their presence ]]

Normative statement in an example
In [2], the "For example" statement contains a normative
statement. It is correct but it seems awkward to find a normative
statement in the middle of an example:
[[ For example, if the User-Agent  header field has been altered, an
X-Device-User-Agent header field must be added with the value of the
received User-Agent header field. ]]

It can be turned into an informative-only example, as the normative
statement is contained in the guideline that precedes it.

I do not think that removing duplicates (be them normative) constitutes
a substantive change, as the conformance statements remain the same.


[4] http://www.w3.org/TR/2009/WD-ct-guidelines-20091006/#sec-via-headers