Suggested kinds of labels (to clarify the discussion)

Vint Cerf vint at
Wed Mar 25 01:45:05 CET 2009

Hi Shawn,

thanks for working this up. I am still stewing about where and how to  
think about the mapping idea and where it goes but your message and  
Erik vdP's are helping to explore ways to model these ideas.


Vint Cerf
1818 Library Street, Suite 400
Reston, VA 20190
vint at

On Mar 24, 2009, at 8:39 PM, Shawn Steele (???) wrote:

> I hope I’m not jumping the gun, but I thought I’d suggest this  
> picture to clarify the definitions for ideas people are talking about.
> I was thinking of the discussion and definitions and think this  
> might work as a starting point. (I added A-Label to a picture from  
> Mark Davis):
> Unicode String (Any old Unicode string, maybe valid or invalid;  
> won't knowuntil tested)
>   - subset: M-Label (maps to a valid U-Label, perhaps with the  
> identity mapping, many to one)
>     - subset: U-Label (canonical)
>       - implies: A-Label (derived from U-Label, one-to-one)
> I think the group pretty much agrees about U-Labels and A-Labels in  
> this context, although there may be some disagreement about which is  
> canonical.
> M-Label is the idea that there are mapped strings (side of the bus  
> strings) that may not be valid U-Labels, but which will map to a  
> valid U-Label.  Eg: this is mapping.  I don’t think it depends on  
> whether mapping is a BCP or Appendix or a different RFC, it’s just  
> the idea of a label that can be mapped.  M-Labels map to U-Labels in  
> a many to 1 relationship.
> I stated that A-Labels are derived from the canonical U-Labels, but,  
> of course, they must also round trip.
> Unicode String is any random string, some of which will be valid IDN  
> labels, others won’t.
> - Shawn
> _______________________________________________
> Idna-update mailing list
> Idna-update at

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