Dave Crocker <dcroc...@bbiw.net> writes: > On 1/27/2021 6:32 PM, Dale Worley via Datatracker wrote: >> Reviewer: Dale Worley >> Review result: Ready with Nits
First to deal with the straightfoward points: >> The emoji(s) express a recipient's summary reaction to the specific >> message referenced by the accompanying In-Reply-To header field. >> [Mail-Fmt]. >> >> This is not specific as to where the In-Reply-To header is. I assume >> you want to say that it is a header of the parent multipart component >> of "Reaction" part. Or perhaps this should be forward-referenced to >> the discussion in section 3. > > I don't understand the concern. An In-Reply-To header field is part of > the message header. That is, it will be in the header of the response > message. Given that we're deailing with multipart messages, an In-Reply-To header could be stuck in the message header but it could also be stuck in the headers of any part. I don't know if it's ever done, but certainly, it's plausible that if I include a reply which I had received as an attachment to another email I send, the In-Reply-To header in the received e-mail would show up as a header to the attachment part, not my message as a whole. In general, the situation is one of unlimited complexity. I'm not particular what rules you want to specify, just that when I'm looking at a part with this Content-Disposition that is somewhere in a multipart structure (possibly without parts), that it's clear which sets of headers I need to examine to find the In-Reply-Header. Now I think in reality, it either has to be in the headers of the part with disposition "reaction", or in the multipart containing that part. But whatever the rule is, it should be stated. >> Reference to unallocated code points SHOULD NOT be treated as an >> error; associated bytes SHOULD be processed using the system default >> method for denoting an unallocated or undisplayable code point. >> >> Code points that do not have the requisite attributes to qualify as >> part of an emoji_sequence should also not be treated as an error, >> although you probably want to allow the system to alternatively >> display them normally (rather than as an unallocated or undisplayable >> code point). > > I think your comment addresses a different issue than the cited text is > meant for, but I also might be misunderstanding. > > For whatever reasons, including not having been allocated by the Unicode > folks, or possibly by running an older system that thinks a code point > is not allocated, there is an issue of how the system should deal with > encountering such a code point. The text here is merely trying to say > "do whatever you do". The text is a constraint, though. It *requires* (sort of) that if the bytes in the part form a character which the receiver considers unallocated, it *should not* reject the whole message as being ill-formed. The implementation has great freedom in how to display the caracter, but the message as a whole "SHOULD NOT be treated as an error". > A different issue is encountering a code-point, here, that is outside of > the emoji-sequence set. The text doesn't try to tell the receiver how to > process bytes that are illegal here. Perhaps that is what you intend, and if so, the text is correct. But it seems to me that if the bytes form a code point that the receiver considers to be allocated but not an emoji, it should be under the same constraint that it should not reject the message as a whole as erroneous. Now for the messy part: > The rule emoji_sequence is inherited from [Emoji-Seq]. It permits > one or more bytes to form a single presentation image. First, let me say I keep a rigid category distinction between bytes/octets and characters. And in this situation, it seems like there are *three* layers of composition between bytes and displayed items: - The UTF-8 encoding groups bytes into code points, which are generally Unicode "characters". - The code points can be composed (by Unicode rules) into characters. As Barry explains, "as creating “á” from “a” plus combining acute accent". But I'm not so familiar with how that is done and how that affects exactly what the word "character" means. (I also do not know whether any emoji code point participates in Unicode composition, but a sender can certainly compose reactions containing code points that participate in composition, and there probably is no guarantee that Unicode will never do such a thing with emoji.) - Groups of characters may be displayed as single images. As Barry explains, "the sort of thing that’s unique to emoji, wherein the emojis for man followed by woman followed by boy, each of which is a separate emoji character that would be displayed as it seems, will often be rendered as a single image of a family". Composing these processes, it takes bytes/octets (the encoded form of the "reaction" part) into a sequence of displayed images. When I wrote my review, I was aware only of the first composition layer. But now, it's not clear to me what the sentence "It permits one or more bytes to form a single presentation image." is intended to say. The combining of bytes to form an image may happen at any of the three layers, and it seems to me that the entire process would be better described as "It permits one or more bytes to form one or more presentation images." But maybe you're trying to say something more specific. 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