Why is \textvisiblespace represented by a rectangle?

Question

I use xelatex, with Ubuntu font, and for some reason I can't insert a \textvisiblespace into my document - all that I get in result is a box: ``. Is there some way to fix that?

Example:

\documentclass[a4paper]{article}
\usepackage{xltxtra}
\setmainfont[Mapping=tex-text]{Ubuntu}
\begin{document}
\textvisiblespace
\end{document}

Answer 1

The font Ubuntu doesn't support the Unicode character 2423. Use

\setmainfont[Mapping=tex-text]{DejaVu Serif}

for example. Another alternative maybe:

\documentclass[a4paper]{article}
\usepackage{fontspec}
\setmainfont[Mapping=tex-text]{Ubuntu}
\newfontface\TVSp{DejaVu Serif}
\def\textvisiblespace{{\TVSp\char"2423}}

\begin{document}
\textvisiblespace
\end{document}

Answer 2

I don't have the font installed, so I'm not sure whether this is what you're after:

1. Redefine \textvisiblespace after loading the Ubuntu font. The following definition is taken from latex.ltx:

   \def\textvisiblespace{%
      \mbox{\kern.06em\vrule height.3ex}%
      \vbox{\hrule width.3em}%
      \hbox{\vrule height.3ex}}
   

2. Capture the contents of \textvisiblespace in a box before loading the new font and restore it afterwards:

   % Document preamble
   \newsavebox{\textvisiblespacebox}
   \begin{lrbox}{\textvisiblespacebox}\textvisiblespace\end{lrbox}
   % Insert font-related changes here
   \def\textvisiblespace{\usebox{\textvisiblespacebox}}
   

   Note that this will fix the setting of \textvisiblespace in \normalfont, so it won't change with size changes like \small (for example).