Define a valueFilter operator to allow specification of additional filtering:

valueFilter Extension usable on DataRequirement 0..*
valueFilter.path string 0..1
valueFilter.searchParam string 0..1
valueFilter.comparator code 1..1 Required binding to { eq, gt, lt, ge, le, sb, ea }
valueFilter.value[x] ( boolean, string, integer, Quantity, Ratio, Range ) 0..1

Invariant: one of path or searchParam SHALL be present