Re: Re: Document Status?

Simon Josefsson <[email protected]> wrote:

> In the particular example of a MUA running in XTERM (or a Unicode unix
> console, for that matter), it will likely not work out as I'm not
> aware of any API between a TTY application and the terminal to query
> which unicode characters it can display, and whether it supports bidi,
> and in that case it seems this paragraph from 6.4 would apply,
> suggesting that MUAs should use ACE anyway:
> 
> ,----
> | If an application decodes an ACE name using ToUnicode but cannot
> | show all of the characters in the decoded name, such as if the
> | name contains characters that the output system cannot display,
> | the application SHOULD show the name in ACE format (which always
> | includes the ACE prefix) instead of displaying the name with the
> | replacement character (U+FFFD).
> `----

The spec says that an application SHOULD NOT show the ACE form if it can
correctly display the Unicode form, and it SHOULD show the ACE form if
it cannot correctly display the Unicode form.  Both recommendations have
equal weight.  If the application cannot know which Unicode characters
can be displayed, then it cannot know which recommendation applies.
If the application is optimistic about the display capabilities, it
risks violating the second recommendation, and if the application is
pessimistic, it risks violating the first recommendation.

The situation is symmetric.  I see no reason to conclude that the spec
favors optimism or pessimism.

> Or is that section only applicable to domain-name slots?  It is not
> clear.

The section begins:

    Any application that might show the user a domain name obtained
    from a domain name slot, such as from gethostbyaddr or part of a
    mail header, will need to be updated if it is to prevent users from
    seeing the ACE.

The section is about what happens when names obtained *from* domain name
slots are shown to users.  Generally, user-visible things are not domain
name slots, they're generic text widgets/terminals.

> Whether section 6.4 must be followed or not at all seems a bit unclear
> after reading the following in section 6.1: "The optional use,
> especially during a transition period, of ACE encodings in the user
> interface is described in section 6.4.".  Is section 6.4 optional?

No, and I can't see anything in section 6.4 that this sentence could
be referring to.  The only description of "the optional use of ACE
encodings in the user interface" that I can find is right there in the
same paragraph as the sentence in question:

    Applications MAY allow input and display of ACE labels, but are not
    encouraged to do so except as an interface for special purposes,
    possibly for debugging.

    Because name labels encoded as ACE name labels can be rendered
    either as the encoded ASCII characters or the proper decoded
    characters, the application MAY have an option for the user to
    select the preferred method of display; if it does, rendering the
    ACE SHOULD NOT be the default.

I wonder if this cross-reference to section 6.4 is an obsolete relic
from an earlier draft that got left in by mistake.  I'll ask Paul and
Patrik about it.

AMC