Books (or other references) for extracting XML data with R

I'll give a course on how to extract data from XML/HTML using R. I do have some practical experience doing this (most of it I learnt by myself, using help from SO), but I'd like some reference to help me organize my thoughts and the cou开发者_StackOverflow社区rse.

Does anyone know any reference (can be a book, lectures notes, websites etc.) on extracting XML/HTML data using R?

Untill now I only found this short introduction to the XML package.

ps.: I know this is not exactly a programming question, but it's related and I've seen related questions here before.

This book has a subsection on XML processing (Section 8.5 XML; p. 254-264)

Gentleman, R., 2009. R Programming for Bioinformatics, Boca Raton: CRC Press.