The real issue: interopability, and a proposal (Was: Consensus Call on Latin Sharp S and Greek Final Sigma)

[Shawn Steele]

> Yes. Existing users made due with "ue" instead of "ü" before IDNA 2003,
> and so on.

Are you sure? ;-)  The biggest difference is that ue == ü didn't exist in IDNA2003, the eszett mapping does.  I also think the upper case form is worth special consideration.

> > so adding Eszett explicitly would put those users at risk.

> How/why? How did adding "ü" put the users of "ue" at risk?

It didn't, ü was already illegal.  Eszett is currently legal, so it changes behavior, not adds it.  Existing users of eszett could potentially be redirected someplace unexpected.  Also the transition period is likely to be a decade, so NEW users of eszett/ss would likely also be potential victims if they only registered one form.

I think I agree that the biggest problem is backwards compatibility.

-Shawn