code: func (s *scalarRange) split() (scalarRange, scalarRange) {
  	if s.start < 0xe000 && s.end > 0xd7ff {
  		return scalarRange{
  				start: s.start,
  				end:   0xd7ff,
  			},
  			scalarRange{
  				start: 0xe000,
  				end:   s.end,
  			}
  	}
  	return nilScalarRange, nilScalarRange
  }
docs: // split this scalar range if it overlaps with a surrogate codepoint