Re: [idn] Figuring out what can be displayed

["Adam M. Costello" <idn.amc+0@nicemice.net.RemoveThisWord>]

John C Klensin <klensin@jck.com> wrote:

> Yes, there are grounds for ignoring a "SHOULD".  That is why we call
> it "SHOULD" and not "MUST".  But we don't describe things that violate
> SHOULDs with phrases like "fully conforming", regardless of the cause

Okay, but I don't see why that's a problem.  If the spec says you SHOULD
do something and it's simply impossible to do it, then you do the best
you can, you don't conclude that you can't implement the spec.  On the
other hand, if the spec had said MUST, then you would have to conclude
that you can't implement the spec.

That said, I don't really care whether the spec says "SHOULD" and
"SHOULD NOT", or "encouraged" and "discouraged", when talking about
choosing which form of label to display.  That would be a technical
change that I don't see the need for, but you can try convincing the
other authors and the area directors.

> please identify at least two operating systems in common use today in
> which an application can accurately determine that it can display a
> particular, arbitrarily-chosen, Unicode character.

This is not my area of expertise, but after poking around on the web, I
found two such platforms:

In Java, Font.canDisplayUpTo(String) will tell you whether a given font
can display a given string.

In MacOS X, NSFont.coveredCharacterSet() will return the set of Unicode
characters that a given font can display.

AMC