def code
      value = attr_val('cda:observation/cda:value/@code') || HQMF::PopulationCriteria::STRAT
      # exclusion population criteria has id of DENOM with actionNegationInd of true
      # special case this to simply handling
      if attr_val('cda:observation/@actionNegationInd')=='true' && value == HQMF::PopulationCriteria::DENOM
        value = HQMF::PopulationCriteria::DENEX
      end
      value.upcase
    end
def code
      value = attr_val('cda:observation/cda:value/@code') || HQMF::PopulationCriteria::STRAT
      # exclusion population criteria has id of DENOM with actionNegationInd of true
      # special case this to simply handling
      if attr_val('cda:observation/@actionNegationInd')=='true' && value == HQMF::PopulationCriteria::DENOM
        value = HQMF::PopulationCriteria::DENEX
      end
      value.upcase
    end
Create a new population criteria from the supplied HQMF entry
 @param [Nokogiri::XML::Element] the HQMF entry
 Get the code for the population criteria
 @return [String] the code (e.g. IPP, DEMON, NUMER, DENEX, DENEXCEP)