eXtensible Time Series (xts)
Provide for uniform handling of R’s different time-based data classes by extending zoo, maximizing native format information preservation and allowing for user level customization and extension, while simplifying cross-class interoperability.

Parse XML (xml2)
Work with XML files using a simple, consistent interface. Built on top of the ‘libxml2’ C library.

Tools for parsing and generating XML within R and S-Plus (XML)
This package provides many approaches for both reading and creating XML (and HTML) documents (including DTDs), both local and accessible via HTTP or FTP. It also offers access to an XPath ‘interpreter’.