% $Id: faq-lab-ref.tex,v 1.4 2011/05/08 10:16:43 rf10 Exp $

\subsection{Labels and references}

\Question[Q-nameref]{Referring to things by their name}

\LaTeX{}'s labelling mechanism is designed for the impersonal world of
the academic publication, in which everything has a number: an
extension is necessary if we are to record the \emph{name} of things
we've labelled.  The two packages available extend the \LaTeX{}
sectioning commands to provide reference by the name of the section.

The \Package{titleref} package is a simple extension which provides
the command \csx{titleref}; it is a stand-alone package~--- don't use it
in a document in which you also need to use \Package{hyperref}.

The \Package{byname} package is part of the \Package{smartref} bundle
and works well with \Package{smartref}, and works (to an extent) with
\Package{hyperref}, but the links it defines are not hyperlinks.

The \Class{memoir} class incorporates the functionality of
\Package{titleref}, but doesn't work with \Package{byname} (though a
search of \Newsgroup{comp.text.tex} on \URL{groups.google.com} will
find a patch to \Package{byname} to remedy the problem).

The \Package{hyperref} bundle includes a package \Package{nameref},
which will work standing alone (i.e., without \Package{hyperref}: of
course, in this mode its references are not hyperlinked).  If you load
\Package{hyperref} itself, \Package{nameref} is automatically loaded.
\Class{Memoir} requires the \Package{memhfixc} when running with
\Package{hyperref}; following the sequence:
\begin{quote}
\begin{verbatim}
\documentclass[...]{memoir}
...
\usepackage[...]{hyperref}
\usepackage{memhfixc}
\end{verbatim}
\end{quote}
\Package{nameref} commands may be used in a \Class{memoir} document.

\Package{Zref} defines a proposed replacement for all of the \LaTeX{}
reference mechanisms, and among other things provides
name-referencing mechanisms:
\begin{quote}
\begin{verbatim}
\usepackage[user,titleref]{zref}
...
\section{hello}\zlabel{sec:one}
The section name is: \ztitleref{sec:one}.
\end{verbatim}
\end{quote}
(One might hope that something of this sort would be the ``way of the
future'', but things move slowly in the \LaTeX{} world: don't hold
your breath.) 

Each of \Package{titleref}, \Package{byname} and \Package{nameref}
defines a reference command with the same name as the package:
\csx{titleref}, \csx{byname} and \csx{nameref}. The \Package{nameref}
package also defines a command \csx{byshortnameref}, which uses the
optional `short' title argument to the chapter and section commands.
(Although it comes from the same author, \Package{zref} \emph{doesn't}
define a short-name variant.)
\begin{ctanrefs}
\item[byname.sty]Distributed with \CTANref{smartref}
\item[hyperref.sty]\CTANref{hyperref}
\item[memoir.cls]\CTANref{memoir}
\item[nameref.sty]Distributed with \CTANref{hyperref}
\item[smartref.sty]\CTANref{smartref}
\item[titleref.sty]\CTANref{titleref}
\item[zref.sty]Distributed as part of \CTANref{oberdiek}[zref]
\end{ctanrefs}

\Question[Q-extref]{Referring to labels in other documents}

When producing a set of inter-related documents, you'll often want to
refer to labels in another document of the set; but \LaTeX{}, of its
own accord, doesn't permit this.

So the package \Package{xr} was written: if you say
\begin{quote}
\begin{verbatim}
\usepackage{xr}
\externaldocument{volume1}
\end{verbatim}
\end{quote}
will load all the references from \File{volume1} into your present
document.

But what if the documents both have a section labelled
``\environment{introduction}'' (likely enough, after all)?  The
package provides a means to transform all the imported labels, so you
don't have to change label names in either document.  For example:
\begin{quote}
\begin{verbatim}
\usepackage{xr}
\externaldocument[V1-]{volume1}
\end{verbatim}
\end{quote}
loads the references from \File{volume1}, but prefixes every one with
the string \texttt{V1-}.  So you would refer to the introduction to volume~1
as:
\begin{quote}
\begin{narrowversion}
\begin{verbatim}
\usepackage{xr}
\externaldocument[V1-]{volume1}
...
... the introduction to volume1
               (\ref{V1-introduction})...
\end{verbatim}
\end{narrowversion}
\begin{wideversion}
\begin{verbatim}
\usepackage{xr}
\externaldocument[V1-]{volume1}
...
... the introduction to volume1 (\ref{V1-introduction})...
\end{verbatim}
\end{wideversion}
\end{quote}
To have the facilities of \Package{xr} working with
\Package{hyperref}, you need \Package{xr-hyper}.  For simple
hyper-cross-referencing (i.e., to a local \acro{PDF} file you've just
compiled), write:
\begin{quote}
\begin{verbatim}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument[V1-]{volume1}
...
... the \nameref{V1-introduction})...
\end{verbatim}
\end{quote}
and the name reference will appear as an active link to the
``introduction'' chapter of \File{volume1.pdf}.

To link to a \acro{PDF} document on the Web, for which you happen to
have the .aux file, write:
\begin{quote}
\begin{wideversion}
\begin{verbatim}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument[V1-]{volume1}[http://mybook.com/volume1.pdf]
...
... the \nameref{V1-introduction})...
\end{verbatim}
\end{wideversion}
\begin{narrowversion}
\begin{verbatim}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument[V1-]{volume1}%
    [http://mybook.com/volume1.pdf]
...
... the \nameref{V1-introduction})...
\end{verbatim}
\end{narrowversion}
\end{quote}
Heiko Oberdiek's experimental \Package{zref} bundle includes a
hyper-crossreferencing mechanism using its \Package{zref-xr} module.
Usage is closely modelled on \Package{xr} and \Package{xr-hyper}; a
trivial example (from a \Newsgroup{comp.text.tex} posting) is
\begin{quote}
\begin{verbatim}
\usepackage{zref-xr,zref-user}
\zexternaldocument*{xr02}
...
\zref{foo}
\end{verbatim}
\end{quote}
The module provides all the facilities of the older packages, and can
deal both with ``traditional'' \LaTeX{} labels and with
\Package{zref}'s style of labels.
\begin{ctanrefs}
\item[xr.sty]Distributed as part of \CTANref{2etools}[xr]
\item[xr-hyper.sty]Distributed with \CTANref{hyperref}[xr-hyper]
\item[zref \nothtml{\rmfamily\itshape}bundle]Distributed as part of
  \CTANref{oberdiek}[zref]
\end{ctanrefs}