Sometimes it is useful to turn off the special meaning of some of the
ten special characters of LaTeX. For instance, when writing
documentation about programs in C, it might be useful to be able to
write some_variable instead of always having to type
some\_variable, especially if you never use any formula and
hence do not need the subscript function. This can be achieved with
the \NotSpecial command.
The characters that you can make non-special are
~ ^ _ # $ &
For instance, to make characters $ and ^ non-special,
you need to use the command
\NotSpecial{\do\$\do\^}
Yes, this syntax is weird, but it makes the implementation much easier.
Note that whereever you put this declaration in the preamble, it will
only be turned on by \begin{document}. This means that you can
still use the regular LaTeX special characters in the
preamble.
Even within the iftex environment the characters
you specified will remain non-special. Sometimes you will want to
return them their full power. This can be done in a tex
environment. It is equivalent to iftex, but also turns on all
ten special LaTeX characters.