Fix bug in dart.sty.

docs/language/dart.sty

 \def\keyword#1{\textbf{#1}}
 \def\builtinId#1{\textbf{#1}}
 \def\comment#1{\textit{#1}}
 \def\capt#1{\rmfamily \caption{#1}}
 \newcommand{\cd}[1]{\textsf{#1}}
 \def\lt{\ensuremath{<}}
 \def\gt{\ensuremath{>}}
 \def\<{\ensuremath{\langle}}
 \def\>{\ensuremath{\rangle}}
 \def\metavar#1{\ensuremath{\mathit{#1}}}
@@ skipping 51 matching lines @@
 \def\THIS{\keyword{this}}
 \def\THROW{\keyword{throw}}
 \def\TRUE{\keyword{true}}
 \def\TRY{\keyword{try}}
 \def\VAR{\keyword{var}}
 \def\VOID{\keyword{void}}
 \def\WHILE{\keyword{while}}
 \def\WITH{\keyword{with}}
 \def\YIELD{\keyword{yield}}
 
-\newenvironment{Q}[1]{{\bf #1}}
-\newenvironment{rationale}[1]{{\it #1}}
-\newenvironment{commentary}[1]{{\sf #1}}
+\newenvironment{Q}[1]{{\bf #1}}{}
+\newenvironment{rationale}[1]{{\it #1}}{}
+\newenvironment{commentary}[1]{{\sf #1}}{}
 
 \newenvironment{dartCode}[1][!ht] {
 %  \begin{verbatim}[#1]
   \def\@programcr{\@addfield\strut}
   \let\\=\@programcr
   \relax\@vobeyspaces\obeylines
 
   \sffamily
 }{
   %\end{verbatim}
@@ skipping 21 matching lines @@
   \hspace{0pt}\marginpar{\raisebox{0.5ex}{\miniscule{\color{LMdim}#1}}}}
 
 % support convenient renewcommand
 \let\OriginalLMHash\LMHash
 
 % define a label, and show the associated logical location marker
 \newcommand{\LMLabel}[1]{%
   \vspace{-\baselineskip}\hspace{0pt}\OriginalLMHash{\raisebox{10ex}{#1}}%
   \label{#1}}
 % ----------------------------------------------------------------------