docs: def vertex_indices_in_segments(self, segments, ret_face_indices=False):
          '''
          Given a list of segment names, return an array of vertex indices for
          all the vertices in those faces.
  
          Args:
              segments: a list of segment names,
              ret_face_indices: if it is `True`, returns face indices
          '''
          import numpy as np
          import warnings
  
          face_indices = np.array([])
          vertex_indices = np.array([])
          if self.segm is not None:
              try:
                  segments = [self.segm[name] for name in segments]
              except KeyError as e:
                  raise ValueError('Unknown segments {}. Consier using Mesh.clean_segments on segments'.format(e.args[0]))
              face_indices = np.unique(np.concatenate(segments))
              vertex_indices = np.unique(np.ravel(self.f[face_indices]))
          else:
              warnings.warn('self.segm is None, will return empty array')
  
          if ret_face_indices:
              return vertex_indices, face_indices
          else:
              return vertex_indices