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

source/uax31.tex

@@ -23,16 +23,16 @@
 \UAX{31} specifies a default syntax for identifiers
 based on properties from the Unicode Character Database, \UAX{44}.
 The general syntax is
-\begin{codeblock}
+\begin{outputblock}
 <Identifier> := <Start> <Continue>* (<Medial> <Continue>+)*
-\end{codeblock}
+\end{outputblock}
 where \tcode{<Start>} has the XID_Start property,
 \tcode{<Continue>} has the XID_Continue property, and
 \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>*