It's often convenient to have commentary text, 'outside' the list,
between successive entries of a list. In the case of
itemize lists this is no problem, since there's never
anything to distinguish successive items, while in the case of
description lists, the item labels are under the user's
control so there's no automatic issue of continuity.
For enumerate lists, the labels are generated
automatically, and are context-sensitive, so the context (in this
case, the state of the enumeration counter) needs to be preserved.
The belt-and-braces approach is to remember the state of the enumeration in your own counter variable, and then restore it when restarting enumerate:
\newcounter{saveenum}
...
\begin{enumerate}
...
\setcounter{saveenum}{\value{enumi}}
\end{enumerate}
<Commentary text>
\begin{enumerate}
\setcounter{enumi}{\value{saveenum}}
...
\end{enumerate}
This is reasonable, in small doses... Problems (apart from sheer
verbosity) are getting the level right ("should I use counter
enumi, enumii, ...") and remembering not to
nest the interruptions (i.e., not to have a separate list, that is
itself interrupted) in the "commentary text").
The mdwlist package defines commands \suspend and
\resume that simplify the process:
\begin{enumerate}
...
\suspend{enumerate}
<Commentary text>
\resume{enumerate}
...
\end{enumerate}
The package allows an optional name (as in
\suspend[id]{enumerate}) to allow you to identify a
particular suspension, and hence provide a handle for manipulating
nested suspensions.
If you're suspending a fancy-enumeration list,
you need to
re-supply the optional "item label layout" parameters required by
the enumerate package when resuming the list, whether by the
belt-and-braces approach, or by the mdwlist
\resume{enumerate} technique. The task is a little tedious
in the mdwlist case, since the optional argument has to be
encapsulated, whole, inside an optional argument to \resume,
which requires use of extra braces:
\begin{enumerate}[\textbf{Item} i]
...
\suspend{enumerate}
<comment>
\resume{enumerate}[{[\textbf{Item} i]}]
...
\end{enumerate}
The enumitem package, in its most recent
release, will allow you to resume lists, at one level only:
\begin{enumerate}
...
\end{enumerate}
<comment>
\begin{enumerate}[resume]
...
\end{enumerate}
which feels just as "natural" as the mdwtools facility,
and has the advantage of playing well with the other excellent
facilities of enumitem.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=interruptlist