From the introduction:
Faceted search has proven to be enormously popular in the real world applications. Faceted search allows user to navigate and access information via a structured facet classification system. Combined with full text search, it provides user with enormous power and flexibility to discover information.
This proposal defines a standardized approach to support the Faceted search in XQuery. It has been designed to be compatible with XQuery 3.0, and is intended to be used in conjunction with XQuery and XPath Full Text 3.0.
Imagine my surprise when after opening Christmas presents with family to see a tweet by XQuery announcing yet another Christmas present:
“Facets”: A new EXPath spec w/extension functions & data models to enable faceted navigation & search in XQuery http://expath.org/spec/facet

The EXPath homepage says:
XPath is great. XPath-based languages like XQuery, XSLT, and XProc, are great. The XPath recommendation provides a foundation for writing expressions that evaluate the same way in a lot of processors, written in different languages, running in different environments, in XML databases, in in-memory processors, in servers or in clients.
Supporting so many different kinds of processor is wonderful thing. But this also contrains which features are feasible at the XPath level and which are not. In the years since the release of XPath 2.0, experience has gradually revealed some missing features.
EXPath exists to provide specifications for such missing features in a collaborative- and implementation-independent way. EXPath also provides facilities to help and deliver implementations to as many processors as possible, via extensibility mechanisms from the XPath 2.0 Recommendation itself.
Other projects exist to define extensions for XPath-based languages or languages using XPath, as the famous EXSLT, and the more recent EXQuery and EXProc projects. We think that those projects are really useful and fill a gap in the XML core technologies landscape. Nevertheless, working at the XPath level allows common solutions when there is no sense in reinventing the wheel over and over again. This is just following the brilliant idea of the W3C’s XSLT and XQuery working groups, which joined forces to define XPath 2.0 together. EXPath purpose is not to compete with other projects, but collaborate with them.
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Be sure to visit the resources page. It has a manageable listing of processors that handle extensions.
What would you like to see added to XPath?
Enjoy!