docs: def first_line_indent(self):
          """
          A |Length| value calculated from the values of `w:ind/@w:firstLine`
          and `w:ind/@w:hanging`. Returns |None| if the `w:ind` child is not
          present.
          """
          ind = self.ind
          if ind is None:
              return None
          hanging = ind.hanging
          if hanging is not None:
              return Length(-hanging)
          firstLine = ind.firstLine
          if firstLine is None:
              return None
          return firstLine