As it is set up now, ptx assumes that the input file is coded
using 8-bit characters, and it may not work well in multibyte locales.
In a single-byte locale, the default regular expression
for a keyword allows foreign or diacriticized letters. Keyword sorting,
however, is still crude; it obeys the underlying character set ordering
quite blindly.
The output of ptx assumes the locale’s character encoding.
For example, with ptx’s -T option, if the locale
uses the Latin-1 encoding you may need a LaTeX directive like
‘\usepackage[latin1]{inputenc}’ to render non-ASCII characters
correctly.
Fold lower case letters to upper case for sorting.