docs: def untldict_normalizer(untl_dict, normalizations):
      """Normalize UNTL elements by their qualifier.
  
      Takes a UNTL descriptive metadata dictionary and a dictionary of
      the elements and the qualifiers for normalization:
      {'element1': ['qualifier1', 'qualifier2'],
       'element2': ['qualifier3']}
      and normalizes the elements with that qualifier.
      """
      # Loop through the element types in the UNTL metadata.
      for element_type, element_list in untl_dict.items():
          # A normalization is required for that element type.
          if element_type in normalizations:
              # Get the required normalizations for specific qualifiers list.
              norm_qualifier_list = normalizations.get(element_type)
              # Loop through the element lists within that element type.
              for element in element_list:
                  # Determine if the qualifier requires normalization.
                  qualifier = element.get('qualifier', None)
                  if qualifier in norm_qualifier_list:
                      content = element.get('content', None)
                      # Determine if there is normalizing for the element.
                      if element_type in ELEMENT_NORMALIZERS:
                          elem_norms = ELEMENT_NORMALIZERS.get(element_type,
                                                               None)
                          # If the qualified element requires a
                          # normalization and has content, replace the
                          # content with the normalized.
                          if qualifier in elem_norms:
                              if content and content != '':
                                  element['content'] = \
                                      elem_norms[qualifier](content)
      return untl_dict