[texhax] Using special characters like _ and " etc

Uwe Lück uwe.lueck at web.de
Mon Dec 29 15:45:32 CET 2008

At 12:57 29.12.08, Syed Faraz Hasan wrote:

>Latex displays everything following an underscore _ or an inverted comma " 
>in italics form. There seems to be a special way of using special 
>characters in the text.

`_' is a standard TeX matter. I experience here and myself that there are 
installations nowadays that don't stop at errors, so many users don't 
realize them! In your .log file, you will find `missing $ inserted'; in the 
old times, TeX stopped to tell you this on screen. `_' is only allowed in 
math mode, not in ordinary text. To get an underscore symbol, type `\_'. 
`_' in text doesn't really switch to italics, rather TeX treats it as `$_' 
and considers all following text a mathematical formula, until it finds a 
`$' or a \par. You also should have noticed that the first character after 
`_' appears as a subscript, that's what `_' is for.

The TeXbook lists all these special characters on page 36. Perhaps looking 
for `category code' helps to find explanations of all of them in various 
documents on TeX and LaTeX.

I am astonished that `"' should switch to something like italics. babel.sty 
and german.sty use it for generating certain language-specific letters or 
characters. Using it for quoting is ``deprecated'' in TeX which was made 
for high typographic ambitions.



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