code: def set_blend_equation(self, mode_rgb, mode_alpha=None):
          
          mode_alpha = mode_rgb if mode_alpha is None else mode_alpha
          self.glir.command('FUNC', 'glBlendEquationSeparate', 
                            mode_rgb, mode_alpha)
docs: Specify the equation for RGB and alpha blending
      
          Parameters
          ----------
          mode_rgb : str
              Mode for RGB.
          mode_alpha : str | None
              Mode for Alpha. If None, ``mode_rgb`` is used.
      
          Notes
          -----
          See ``set_blend_equation`` for valid modes.