docs: def _pluralize(value, item_key):
      """"Force the value of a datacite3 key to be a list.
  
      >>> _pluralize(xml_input['authors'], 'author')
      ['Sick, Jonathan', 'Economou, Frossie']
  
      Background
      ----------
      When `xmltodict` proceses metadata, it turns XML tags into new key-value
      pairs whenever possible, even if the value should semantically be treated
      as a `list`.
  
      For example
  
      .. code-block:: xml
  
         <authors>
           <author>Sick, Jonathan</author>
         </authors
  
      Would be rendered by `xmltodict` as::
  
         {'authors': {'author': 'Sick, Jonathan'}}
  
      While
  
      .. code-block:: xml
  
         <authors>
           <author>Sick, Jonathan</author>
           <author>Economou, Frossie</author>
         </authors
  
      is rendered by `xmltodict` as::
  
         {'authors': [{'author': ['Sick, Jonathan', 'Economou, Frossie']}}
  
      This function ensures that values are *always* lists so that they can be
      treated uniformly.
  
      Parameters
      ----------
      value : obj
          The value of a key from datacite metadata extracted by `xmltodict`.
          For example, `xmldict['authors']`.
      item_key : str
          Name of the tag for each item; for example, with the `'authors'` key
          the item key is `'author'`.
  
      Returns
      -------
      item_values : list
          List of values of all items.
      """
      v = value[item_key]
      if not isinstance(v, list):
          # Force a singular value to be a list
          return [v]
      else:
          return v