docs: def _broadcast_compat_variables(*variables):
      """Create broadcast compatible variables, with the same dimensions.
  
      Unlike the result of broadcast_variables(), some variables may have
      dimensions of size 1 instead of the the size of the broadcast dimension.
      """
      dims = tuple(_unified_dims(variables))
      return tuple(var.set_dims(dims) if var.dims != dims else var
                   for var in variables)