Yep, now it finally works. Certainly it requires a few more lines. I was
going to rewrite some TikZ code which was too dependent on LaTeX and
xstring was the last stone on the shoe. Thank you a lot, Phelype and
Wolfgang (I didn't know about push/popmacro either and now it's in my to-do
readings).

Jairo :D

El mar., 7 de jul. de 2020 a la(s) 16:31, Phelype Oleinik (
phe.h.o1@gmail.com) escribió:

> On Tue, Jul 7, 2020 at 6:21 PM Jairo A. del Rio <jairoadelrio6@gmail.com>
> wrote:
> >
> > Thank, Wolfgang! Both methods work, but both fail with the following
> example:
> >
> > \pushmacro\unexpanded
> > \let\unexpanded\normalunexpanded
> > \input xstring
> > \popmacro\unexpanded
> > \starttext
> > \StrGobbleLeft{bcdef}{4}
> > \stoptext
> >
> > The log says:
> >
> > tex error > tex error on line 6 in file ./tests.tex: ! This can't happen
> (prefixed command)
> >
> >
> > <argument> \unexpanded {
> >
> > f}
> >
> > \xs_execfirst #1#2->#1
> >
> > However, some others work.
>
> As I said, the internals of `xstring` still use \unexpanded which, after
> you do \popmacro\unexpanded, will mean e-TeX's \protected, rather than
> \unexpanded, which are quite different.  To be on the safe side, you'd
> need to wrap every `xstring` command in
>     \pushmacro\unexpanded
>     \let\unexpanded\normalunexpanded
>     <xstring stuff>
>     \popmacro\unexpanded
> to make sure that \unexpanded means what `xstring` expects.
>
> The *proper* way to make `xstring` work in ConTeXt would be something
> like Circuitikz does:
>     \ifcsname normalunexpanded\endcsname
>       \let\pgfcircutil@unexpanded\normalunexpanded
>     \else
>       \let\pgfcircutil@unexpanded\unexpanded
>     \fi
> then use \pgfcircutil@unexpanded in the code, which will always have the
> same meaning.  That, of course, requires an update to `xstring`.
>
> Phelype
>
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