Why does \xspace behave differently for parenthesis vs. braces/brackets?

Question

Consider:

\documentclass{article}
\usepackage{xspace}
\begin{document}
(something\xspace)

[something\xspace]

\{something\xspace\}
\end{document}

Or more to the point:

\documentclass{article}
\usepackage{xspace}
\newcommand{\something}{something\xspace}
\begin{document}
(\something)

[\something]

\{\something\}
\end{document}

Either of these yields:

So the question is, why does \xspace produce a space before ] and } but not )? I find this very annoying. I would much rather it produces no space in any of these three circumstances. I know I can get rid of the space by using \xspace{} or \something{}, but it sort of defeats the purpose, which is primarily to define my own macros so that I don't need to think about whether I need {} afterwards, and can just use the macro as if it were a word.

Do people consider this a bug? And if so, how should I report it?

Answer 1

The author(s) of xspace didn't included ] and \} in the list of exceptions. Why? No Idea. But there is \xspaceaddexceptions which allows you to add them:

\documentclass{article}
\usepackage{xspace}
\xspaceaddexceptions{]\}}
\newcommand{\something}{something\xspace}
\begin{document}
(\something)

[\something]

\{\something\}
\end{document}

Result:

Answer 2

xspace uses a list of exceptions to decide when to add a space; the original definition of the list is:

\def\@xspace@exceptions@tlp{%
,.’/?;:!~-)\ \/\bgroup\egroup\@sptoken\space\@xobeysp
\footnote\footnotemark
}

As you see, ) is included in the lsit, but } and ] are not, so xspace will add a space. If you want to remove the space for this characters, add } and ] to the list by using \xspaceaddexceptions{]\}}.