Unknown variables in XPATH (2.0)

I have been requested to provide, in the implementation of XPath 2.0
that I am developing), to provide the facility that any variable not
defined in some specific way (such as added to the static context by
an xsl:variable declaration) be evaluated as boolean
false(). Implementing this is easy enough. My question is, do people
consider this a valid interpretation of the draft recommendation, or
should I make it an optional feature?
-- 
Colin Paul Adams
Preston Lancashire

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