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## 3.7 `xr`: Cross-Document References

The LaTeX package `xr` makes it possible to create references to labels defined in external documents. The preamble of a document using `xr` will contain something like this:

 ```\usepackage{xr} \externaldocument[V1-]{volume1} \externaldocument[V3-]{volume3} ```

and we can make references to any labels defined in these external documents by using the prefixes ‘V1-’ and ‘V3-’, respectively.

RefTeX can be used to create such references as well. Start the referencing process normally, by pressing C-c ). Select a label type if necessary. When you see the label selection buffer, pressing x will switch to the label selection buffer of one of the external documents. You may then select a label as before and RefTeX will insert it along with the required prefix.

For this kind of inter-document cross-references, saving of parsing information and the use of multiple selection buffers can mean a large speed-up (see Optimizations).

This document was generated by Ralf Angeli on August, 9 2009 using texi2html 1.78.