p:option/@values should also accept references to static options

[xatapult]

The p:option/@values attribute is defined as a list of atomic values.

There are situations where you would like to define the acceptable values as static options (to prevent magic values). So the @values attribute should probably also accept references to static options.

Or more in general: Any XPath expressions that can be computed at compile time (the same restriction as there is for the values of static options).