How can I use math inside a label in Description in a beamer doc?

Question

I'm describing regular expressions, and I would like to have items like this:

\documentclass[10pt,hyperref={pdfpagelabels=false}]{beamer}
\usepackage[utf8x]{inputenc}
\usepackage{default}

\mode<presentation>
{
 \usetheme{Warsaw}
 \setbeamertemplate{background canvas}[vertical shading][bottom=white!10,top=blue!10]
 \setbeamercovered{transparent}
}

\usepackage[brazil]{babel}
\usepackage[T1]{fontenc}
\usepackage[scaled=.80]{helvet}
\usepackage{graphicx}
\setbeamertemplate{caption}[numbered]   

\begin{document}
\section{Search}
\subsection{Regular Exp}
 \begin{frame}[allowframebreaks]{\texttt{Regular Expressions} Operators}{Powerfull}
  \texttt{Regular Expressions} (\texttt{RE}) are good:
  \begin{description}
   \item[\textasciicircum]  Matches the beginning of the line
   \item[\textbackslash] Escape character
   \item[[]] Group characters
   \item[\textbackslash( \textbackslash)] Hell
   \item[$\textbackslash< \textbackslash> $] Hey.
%   \item[{$[:\mathtt{upper}:]$}] Same as $[A-Z]$.
  \end{description}
 \end{frame}
\end{document}

But some of them seem not to work. Some variants I've tried (with ] outside math) gave me half of the item in the correct font/color, and the last char ] in black as if it was normal text.

Please, how can I get this done?

-- Edited: minimal working example added.

Answer 1

Update answer

In the comments above it turned out that the @DrBeco uses TeX Live 2009. I suppose it was installed by the default repository of the unix system. However this version isn't up to date. I really recommend to install TeX Live 2011. In this way you can use the update manager tlmgr to get the newest version of nearly every package. If you are using TeX Live 2011 your example will work well.

I want to provide another hint. Don't use utf8x. Some explanation can be found here:

• utf8x vs. utf8 (inputenc)

Original answer

Why do you use commands like \textasciicircum or \textbackslash in math mode? The first part of the command indicates text not math.

\documentclass{article}
\begin{document}
  \begin{description}
   \item[\textasciicircum] Matches the beginning of the line
   \item[\textbackslash] Escape character
   \item[{[]}] Group characters
   \item[\textbackslash( \textbackslash) ] Save to a buffer
   \item[{$[:\mathtt{upper}:]$}] Same as $[A-Z]$.
  \end{description}
\end{document}

The same result with beamer:

\documentclass[10pt,hyperref={pdfpagelabels=false}]{beamer}
\begin{document}
\begin{frame}
\setbeamerfont{description item}{family=\ttfamily}
  \begin{description}
   \item[\textasciicircum]  Matches the beginning of the line
   \item[\textbackslash] Escape character
   \item[{[]}] Group characters
   \item[\textbackslash( \textbackslash) ] Save to a buffer
   \item[{$[:\mathtt{upper}:]$}] Same as $[A-Z]$.
  \end{description}
\end{frame}
\end{document}

Answer 2

I get what's expected with

\begin{description}
\item[\textasciicircum]  Matches the beginning of the line
\item[\textbackslash] Escape character
\item[{[]}] Group characters
\item[\textbackslash( \textbackslash)] Hell
\item[$\textbackslash< \textbackslash> $] Hey.
\item[{$[:\mathtt{upper}:]$}] Same as $[A-Z]$.
\end{description}

However, math mode is not necessary (and even wrong) in items number 5 and 6. Notice also the braces in the fourth item.

Here's how I would input the description list:

\begin{description}
\item[\texttt{\textasciicircum}]  Matches the beginning of the line
\item[\texttt{\textbackslash}] Escape character
\item[\texttt{[]}] Group characters
\item[\texttt{\textbackslash( \textbackslash)}] Hell
\item[\texttt{\textbackslash< \textbackslash>}] Hey.
\item[\texttt{[:upper:]}] Same as \texttt{[A-Z]}.
\end{description}

which will use typewriter type for the regular expression samples.

If all your description labels in a frame are to be typeset in typewriter type, then Marco Daniel's suggestion is good, but brackets must be hidden:

\setbeamerfont{description item}{family=\ttfamily} % this will hold until \end{frame}
\begin{description}
\item[\textasciicircum]  Matches the beginning of the line
\item[\textbackslash] Escape character
\item[{[]}] Group characters
\item[\textbackslash( \textbackslash)] Hell
\item[\textbackslash< \textbackslash>] Hey.
\item[{[:upper:]}] Same as \texttt{[A-Z]}.
\end{description}