code: def classifications_for_layer(self):
          
          subcategory_key = self.parent.step_kw_subcategory.\
              selected_subcategory()['key']
          layer_purpose = self.parent.step_kw_purpose.selected_purpose()
          if layer_purpose in [layer_purpose_hazard, layer_purpose_exposure]:
              classifications = []
              selected_unit = self.parent.step_kw_unit.selected_unit()
              for classification in get_classifications(subcategory_key):
                  if selected_unit is None:
                      # we are using classified data, so let's allow all
                      # classifications
                      classifications.append(classification)
                  elif 'multiple_units' not in classification:
                      # this classification is not multiple unit aware, so let's
                      # allow it
                      classifications.append(classification)
                  elif selected_unit in classification['multiple_units']:
                      # we are using continuous data, and this classification
                      # supports the chosen unit so we allow it
                      classifications.append(classification)
              return classifications
          else:
              # There are no classifications for non exposure and hazard
              # defined yet
              return []
docs: Return a list of valid classifications for a layer.
  
          :returns: A list where each value represents a valid classification.
          :rtype: list