Babel, a multilingual package for use with LATEX's ... - linsrv.net

451 \def\noexpand\@sanitize{\@sanitize\@makeother#1}%
452 \fi}%
453 \x}
The macro \x contains at this moment the following:
\endgroup\def\dospecials{old contents \do〈char〉}.
If \@sanitize is defined, it contains an additional definition of this macro. The last
thing we have to do, is the expansion of \x. Then \endgroup is executed, which
restores the old meaning of \x, \do and \@makeother. After the group is closed,
the new definition of \dospecials (and \@sanitize) is assigned.
\bbl@remove@special
The companion of the former macro is \bbl@remove@special. It is used to remove
a character from the set macros \dospecials and \@sanitize.
To keep all changes local, we begin a new group. Then we define a help macro \x,
which expands to empty if the characters match, otherwise it expands to its
nonexpandable input. Because T E X inserts a \relax, if the corresponding \else or
\fi is scanned before the comparison is evaluated, we provide a ‘stop sign’ which
should expand to nothing.
With the help of this macro we define \do and \make@other.
The rest of the work is similar to \bbl@add@special.
454 \def\bbl@remove@special#1{%
455 \begingroup
456 \def\x##1##2{\ifnum‘#1=‘##2\noexpand\@empty
457 \else\noexpand##1\noexpand##2\fi}%
458 \def\do{\x\do}%
459 \def\@makeother{\x\@makeother}%
460 \edef\x{\endgroup
461 \def\noexpand\dospecials{\dospecials}%
462 \expandafter\ifx\csname @sanitize\endcsname\relax \else
463 \def\noexpand\@sanitize{\@sanitize}%
464 \fi}%
465 \x}
7.4 Shorthands
\initiate@active@char
A language definition file can call this macro to make a character active. This
macro takes one argument, the character that is to be made active. When the
character was already active this macro does nothing. Otherwise, this macro
defines the control sequence \normal@char〈char〉 to expand to the character in its
‘normal state’ and it defines the active character to expand to \normal@char〈char〉
by default (〈char〉 being the character to be made active). Later its definition can
be changed to expand to \active@char〈char〉 by calling \bbl@activate{〈char〉}.
For example, to make the double quote character active one could have
\initiate@active@char{"} in a language definition file. This defines " as
\active@prefix "\active@char" (where the first " is the character with its
original catcode, when the shorthand is created, and \active@char" is a single
token). In protected contexts, it expands to \protect " or \noexpand " (ie, with
the original "); otherwise \active@char" is executed. This macro in turn expands
to \normal@char" in “safe” contexts (eg, \label), but \user@active" in normal
“unsafe” ones. The latter search a definition in the user, language and system
levels, in this order, but if none is found, \normal@char" is used. However, a
deactivated shorthand (with \bbl@deactivate is defined as
\active@prefix "\normal@char".
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