[uaxid] Mark code that's not to be highlighted.

Author: Eelis

source/uax31.tex

@@ -33,8 +33,8 @@
 \tcode{<Medial>} is a list of characters permitted between continue characters.
 For \Cpp{} we add the character \unicode{005f}{low line}, or \tcode{_},
 to the set of permitted \tcode{<Start>} characters,
-the \tcode{<Medial>} set is empty, and
-the \tcode{<Continue>} characters are unmodified.
+the \noncxxtcode{<Medial>} set is empty, and
+the \noncxxtcode{<Continue>} characters are unmodified.
 In the grammar used in \UAX{31}, this is
 \begin{outputblock}
 <Identifier> := <Start> <Continue>*