XForms CR - 3.3.1etc "XPath Extension Functions"

In 3.3.1 (and elsewhere in the CR) reference is made to "XPath Extension 
Functions".

As I recall, the XPath 1.0 Recommendation does not define any mechanism for 
creating extension functions.

Perhaps the XForms WG intended to reference a mechanism defined other than in 
the XPath 1.0 Recommendation?

Andrew Watt