docs: def from_conll(this_class, text):
          """Construct a Token from a line in CoNLL-X format."""
          fields = text.split('\t')
          fields[0] = int(fields[0]) # index
          fields[6] = int(fields[6]) # head index
          if fields[5] != '_': # feats
              fields[5] = tuple(fields[5].split('|'))
          fields = [value if value != '_' else None for value in fields]
          fields.append(None) # for extra
          return this_class(**dict(zip(FIELD_NAMES_PLUS, fields)))