\ignorespacesafterend
Suppose that you want to define an environment for displaying text that is numbered as an equation. A straightforward way to do this is as follows:
\newenvironment{texteqn}
{\begin{equation}
\begin{minipage}{0.9\linewidth}}
{\end{minipage}
\end{equation}}
However, if you have tried this then you will probably have noticed
that it does not work perfectly when used in the middle of a paragraph
because an inter-word space appears at the beginning of the first
line after the environment.
There is now an extra command (with a very long name) available that you can use to avoid this problem; it should be inserted as shown here:
\newenvironment{texteqn}
{\begin{equation}
\begin{minipage}{0.9\linewidth}}
{\end{minipage}
\end{equation}
\ignorespacesafterend}