docs: def map_indices_parent2child(child, parent_indices):
      """Map parent RTDCBase event indices to RTDC_Hierarchy
  
      Parameters
      ----------
      parent: RTDC_Hierarchy
          hierarchy child
      parent_indices: 1d ndarray
          hierarchy parent (`child.hparent`) indices to map
  
      Returns
      -------
      child_indices: 1d ndarray
          child indices
      """
      parent = child.hparent
      # filters
      pf = parent.filter.all
      # indices in child
      child_indices = []
      count = 0
      for ii in range(len(pf)):
          if pf[ii]:
              # only append indices if they exist in child
              if ii in parent_indices:
                  # current child event count is the child index
                  child_indices.append(count)
              # increment child event count
              count += 1
  
      return np.array(child_indices)