### 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 xr was written: if you say

>     \usepackage{xr}
>     \externaldocument{volume1}

will load all the references from volume1 into your present document.

But what if the documents both have a section labelled "`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:

>     \usepackage{xr}
>     \externaldocument[V1-]{volume1}

loads the references from volume1, but prefixes every one with the string `V1-`. So you would refer to the introduction to volume 1 as:

>     \usepackage{xr}
>     \externaldocument[V1-]{volume1}
>     ...
>     ... the introduction to volume1 (\ref{V1-introduction})...

To have the facilities of xr working with hyperref, you need xr-hyper. For simple hyper-cross-referencing (i.e., to a local PDF file you've just compiled), write:

>     \usepackage{xr-hyper}
>     \usepackage{hyperref}
>     \externaldocument[V1-]{volume1}
>     ...
>     ... the \nameref{V1-introduction})...

and the name reference will appear as an active link to the "introduction" chapter of volume1.pdf.

To link to a PDF document on the Web, for which you happen to have the .aux file, write:

>     \usepackage{xr-hyper}
>     \usepackage{hyperref}
>     \externaldocument[V1-]{volume1}[http://mybook.com/volume1.pdf]
>     ...
>     ... the \nameref{V1-introduction})...

`xr.sty`
  Distributed as part of macros/latex/required/tools (zip, browse)
`xr-hyper.sty`
  Distributed with macros/latex/contrib/hyperref (zip, browse)

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=extref