[texhax] HTML specials with '_' character

[Michael M. Tung]

Dear Oleg,

many thanks! Your detailed reply resolved my last problems.

Best, Mike

Oleg Katsitadze [olegkat at gmail.com] wrote:
> On Sun, Feb 17, 2008 at 08:27:54PM +0100, Michael M. Tung wrote:
> > \mailto which now works perfectly!
> 
> It was only working by coincidence (see below).
> 
> > \def\@mailto#1{
> 
> Note that in plain TeX, catcode of @ is 12, which means it is not a
> valid character in multi-letter command names.  It can only be used
> for a single-letter command (\@), and that's exactly what the above
> \def defines.  If you put \show\@ after the definition, you'll see:
> 
>   > \@=macro:
>   mailto#1-> \special {html:<a href="mailto:#1">}{\tt #1} \special {html:</a>} \c
>   atcode `\_=8\relax .
>   l.9 \show\@
> 
> That is, \@ is a macro taking one argument which should be preceded
> ("delimited on the left") with letters m-a-i-l-t-o.  And this was
> perfectly fine until you redefined it here:
> 
> > \def\@href#1#2{
> 
> Now, \@ is a macro taking two arguments which should be preceded with
> letters h-r-e-f, so when we say \@mailto, TeX complains because it
> cannot find href following \@.
> 
> So, why use @ in macro names?  That's the common trick to make
> "hidden" macros, which can't be called by the end user.  For this to
> work, you have to temporarily change catcode of @ to 11 ("letter") so
> that you can use it to define your hidden macros (this is the part
> Reinhard omitted), and when you are done, change the catcode back to
> 12, to prevent users from calling hidden macros.  Something like:
> 
>   \catcode`@=11
>   \def\@mailto#1{...}
>   <other definitions of (or calling the) hidden macros>
>   \catcode`@=12
> 
>   <user space>
> 
> HTH,
> Oleg

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