docs: def build(self):
          """Builds the `HelicalHelix`."""
          helical_helix = Polypeptide()
          primitive_coords = self.curve_primitive.coordinates
          helices = [Helix.from_start_and_end(start=primitive_coords[i],
                                              end=primitive_coords[i + 1],
                                              helix_type=self.minor_helix_type,
                                              aa=1)
                     for i in range(len(primitive_coords) - 1)]
          residues_per_turn = self.minor_residues_per_turn(
              minor_repeat=self.minor_repeat)
          if residues_per_turn == 0:
              residues_per_turn = _helix_parameters[self.minor_helix_type][0]
          if self.minor_handedness == 'l':
              residues_per_turn *= -1
          # initial phi_c_alpha value calculated using the first Helix in helices.
          if self.orientation != -1:
              initial_angle = dihedral(numpy.array([0, 0, 0]),
                                       primitive_coords[0],
                                       primitive_coords[1],
                                       helices[0][0]['CA'])
          else:
              initial_angle = dihedral(
                  numpy.array([0, 0, primitive_coords[0][2]]),
                  primitive_coords[0],
                  numpy.array([primitive_coords[0][0],
                               primitive_coords[0][1], primitive_coords[1][2]]),
                  helices[0][0]['CA'])
          # angle required to achieve desired phi_c_alpha value of self.phi_c_alpha.
          addition_angle = self.phi_c_alpha - initial_angle
          for i, h in enumerate(helices):
              angle = (i * (360.0 / residues_per_turn)) + addition_angle
              h.rotate(angle=angle, axis=h.axis.unit_tangent,
                       point=h.helix_start)
              helical_helix.extend(h)
          helical_helix.relabel_all()
          self._monomers = helical_helix._monomers[:]
          for monomer in self._monomers:
              monomer.ampal_parent = self
          return