*** References to external documents.
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.