docs: def moreland_adjusthue (msh, m_unsat):
      """Moreland's AdjustHue procedure to adjust the hue value of an Msh color
      based on ... some criterion.
  
      *msh* should be of of shape (3, ). *m_unsat* is a scalar.
  
      Return value is the adjusted h (hue) value.
  
      """
      if msh[M] >= m_unsat:
          return msh[H] # "Best we can do"
  
      hspin = (msh[S] * np.sqrt (m_unsat**2 - msh[M]**2) /
               (msh[M] * np.sin (msh[S])))
  
      if msh[H] > -np.pi / 3: # "Spin away from purple"
          return msh[H] + hspin
      return msh[H] - hspin