*** References to external documents.<BR>
The LaTeX package `xr' allows to cross-reference labels in external
documents.  RefTeX can provide information about the external
documents as well.  To use this feature, set up the \externaldocument
macros required by the `xr' package and rescan the document with
RefTeX.  The external labels can then be accessed with the `x' key in
the selection buffer provided by `reftex-reference' (bound to `C-c )').
The `x' key also works in the table of contents buffer.
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