Although the term XRX was originally intended to connote the three standards - XForms, REST and XQuery, the term has been used by different people in different ways and has a spectum of defintions from very broad to very specific.
One the most broad definitions, XRX can connote any web application architecture that stores XML on the client with REST interfaces to XML on the server. The only aspect that these architectures have in common is that they use a no-shredding system to store and edit records.
One of the most specific definitions and the definition that is used in this book is the use of XForms on the client, REST interfaces and XQuery on the server. This implies that many of the features of these standards are integral to the overall solution.