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Date:         Mon, 30 Jun 2014 09:05:59 -0400
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From: "Joel C. Salomon" <joelcsalomon@GMAIL.COM>
Subject: Re: Case changing operations
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Status: R

On 6/30/2014 4:22 AM, Joseph Wright wrote:
> The versions with one argument do a relatively simple
> language-insensitive mapping:
>
>   \tl_lower_case:n { HELLO } =3D> "hello"
>   \tl_upper_case:n { hello } =3D> "HELLO"
>   \tl_mixed_case:n { HELLO } =3D> "Hello"
>
> while the two-argument versions can do language-dependent changes, such
> as dotted/dotless-i/I handling in Turkish:
>
>   \tl_upper_case:nn { tr } { i } =3D> "=C4=B0"

There=E2=80=99s an important use-case that seems not to have been address=
ed,
but perhaps this is better handled in a different layer:
mixed-language strings.

For example, consider a document with the title, =E2=80=9CThe Interesting=
 Life
of Rag=C4=B1p Hul=C3=BBsi =C3=96zdem=E2=80=9D (to chose the first Turkish=
 name I could find
with both dotted i and dotless =C4=B1). Somehow, within the \title{}
declaration, the change of language must be indicated so that (e.g.)
at the top of the page this will be transformed to =E2=80=9CTHE INTERESTI=
NG
LIFE OF RAGIP HUL=C3=9BS=C4=B0 =C3=96ZDEM=E2=80=9D and not =E2=80=9CTHE I=
NTEREST=C4=B0NG L=C4=B0FE =E2=80=A6=E2=80=9D nor =E2=80=9C=E2=80=A6
LIFE OF RAGIP HUL=C3=9BSI =E2=80=A6=E2=80=9D.

A similar situation arises in German where within geographical names
=E2=80=98=C3=9F=E2=80=99 should capitalize to the recently-defined =E2=80=
=98=E1=BA=9E=E2=80=99, not =E2=80=98SS=E2=80=99.
(According to <http://en.wikipedia.org/wiki/Capital_=E1=BA=9E>, this rule=
 was
adopted in 2010.)

As I said, this is probably best handled in a separate layer:  Code
that capitalizes user-provided text would need to defer to the LaTeX3
equivalent of Babel, which would scan the text for user-level
language-change commands, and (among other things) call
\tl_upper_case:nn with the appropriate language argument.  But I think
it=E2=80=99s important that the interface to the casing functions being
defined now be aware of the way they will likely be used.

=E2=80=94Joel