[Standards] IDNA text for rfc3920bis

Peter Saint-Andre stpeter at jabber.org
Thu Apr 12 22:45:27 UTC 2007

Joe Hildebrand and I have been working on revised text regarding 
internationalized domain names in XMPP. RFC 3920 says:


    A domain identifier MUST be an
    "internationalized domain name" as defined in [IDNA], to which the
    Nameprep [NAMEPREP] profile of stringprep [STRINGPREP] can be applied
    without failing.  Before comparing two domain identifiers, a server
    MUST (and a client SHOULD) first apply the Nameprep profile to the
    labels (as defined in [IDNA]) that make up each identifier.


I don't have time to describe the errors in detail, but if you carefully 
read RFCs 3490 and 3491 you will realize that the text in RFC 3920 is 
wrong. Therefore, after much back and forth, Joe and I would like to 
propose the following text:


    A domain identifier MUST be an "internationalized domain name" as
    defined in [IDNA], that is, "a domain name in which every label is an
    internationalized label".  When preparing a text label (consisting of
    a sequence of Unicode code points) for representation as an
    internationalized label in the process of constructing an XMPP domain
    identifier or comparing two XMPP domain identifiers, an application
    MUST ensure that for each text label it is possible to apply without
    failing the ToASCII operation specified in [IDNA] with the
    UseSTD3ASCIIRules flag set (thus forbidding ASCII code points other
    than letters, digits, and hyphens).  If the ToASCII operation can be
    applied without failing, then the label is an internationalized
    label.  An internationalized domain name (and therefore an XMPP
    domain identifier) is constructed from its constituent
    internationalized labels by following the rules specified in [IDNA].
    Note: The ToASCII operation includes application of the [NAMEPREP]
    profile of [STRINGPREP] and encoding using the algorithm specified in
    [PUNYCODE]; for details, see [IDNA].




Peter Saint-Andre
XMPP Standards Foundation

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