[XQuery] IBM-XQ-005: Selective implementation of axes

(IBM-XQ-005) Section 2.6.3 (Full Axis Feature): The phrase "raises a 
static error" should be changed to "may raise a static error", to denote 
that an implementation may selectively implement some of the reverse axes 
of XPath even though it does not claim to support the Full Axis Feature.

--Don Chamberlin