Add some AD suggested wording to content coding decoding discussion (#3367)

I think it captures what was
described in the issue and on the subsequent PR.

Fixes #3356

---------

Co-authored-by: Mike Bishop <[email protected]>

Author: LPardue

draft-ietf-httpbis-unencoded-digest.md

@@ -236,11 +236,15 @@ needs to decode all encodings in order before validation.
 
 Since the digest is calculated on unencoded representation bytes, validation of
 a message with content codings (as described above) can only succeed where the
-decoded output produces the same byte sequence as the input. While many
-registered content codings behave this way, there is no requirement for them to
-do so and it remains a possibility that decoding could produce a
-different byte sequence. In order to avoid unintended validation failures, care
-is advised when selecting content codings for use with `Unencoded-Digest`.
+decoded output produces the same byte sequence as the input. While {{Section
+8.4.1 of !HTTP=RFC9110}} describes content codings to operate "without loss of
+information", that doesn't necessarily mean a byte-for-byte equivalence. A
+content coding could perform semantically-meaningless
+transformations that nevertheless result in a decoded byte sequence that does
+not exactly match the original unencoded representation. In order to avoid
+unintended validation failures, care is advised when selecting content codings
+for use with `Unencoded-Digest`; that said, most registered content codings do provide
+byte-for-byte equivalence and are appropriate.
 
 
 # Integrity Fields are Complementary