M-label definition

[Eric Brunner-Williams]

that was my understanding, U is a subset of M.

Vint Cerf wrote:
> won't making M-label a subset of U-label destroy an important property  
> of U-label as defined in IDNA2008?
>
> Under IDNA2008 there is a one-to-one mapping of every U-label to A- 
> label and vice-versa, without any mapping.
>
> M-label needs mapping to become a U-label and is thus a superset, I  
> believe.
>
> Vint Cerf
> Google
> 1818 Library Street, Suite 400
> Reston, VA 20190
> 202-370-5637
> vint at google.com
>
>
>
>
> On Apr 7, 2009, at 11:27 PM, YAO Jiankang wrote:
>
>   
>> ----- Original Message -----
>> From: "Erik van der Poel" <erikv at google.com>
>> To: "Paul Hoffman" <phoffman at imc.org>
>> Cc: <idna-update at alvestrand.no>; "John C Klensin" <klensin at jck.com>;  
>> "Lisa Dusseault" <lisa.dusseault at gmail.com>
>> Sent: Wednesday, April 08, 2009 10:19 AM
>> Subject: Re: M-label definition
>>
>>
>>
>>     
>>>>> "An M-label is a string that can be mapped into a
>>>>> [valid] U-label. It may be a U-label, since those
>>>>> trivially map into themselves. The category of U-label
>>>>> is a proper subset of the category of M-label." (Mark
>>>>> and others).
>>>>>           
>>> So, one possibility for M-label is to make it correspond to an
>>> IDNA2003 "internationalized label", which would make the set of
>>> M-labels a superset of U-labels. (The other possibility mentioned by
>>> John is: [<set of U-labels> + <set of M-labels>] corresponds to <set
>>> of IDNA2003 internationalized labels>.)
>>>       
>> another view:
>>
>> [<set of U-labels> + <set of A-labels>] corresponds to <set of  
>> IDNA2003 internationalized labels> since IDNA2003 internationalized  
>> labels including all the forms of all valid IDNA2003  
>> internationalized labels.
>>
>> M-label is a subset of U-label instead of superset. M-label is a  
>> special U-label which must do some mapping before being transformed  
>> into A-label or doing some lookup.
>>
>>
>>
>> YAO Jiankang
>>
>>
>>
>>
>>
>>     
>>> Does this make sense?
>>>
>>> Erik
>>>
>>> On Tue, Apr 7, 2009 at 5:31 PM, Paul Hoffman <phoffman at imc.org>  
>>> wrote:
>>>       
>>>> At 4:59 PM -0700 4/7/09, Lisa Dusseault wrote:
>>>>         
>>>>> I'm not certain a new term needs to be introduced. If we're talking
>>>>> about a string that is invalid as a label, giving it that term  
>>>>> seems
>>>>> to legitimize it. If we're talking about a string that may or may  
>>>>> not
>>>>> be valid, that's just "a string"
>>>>>           
>>>> Good catch. John's second option was:
>>>>
>>>>         
>>>> When I supported it, I was thinking of it as "...a valid U-label",  
>>>> that is, without the "valid" being optional.
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>>>>         
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>>>       
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>
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