code: func (r *KeyRange) IsPoint() bool {
  	if len(r.StartKey) != len(r.EndKey) {
  		// Works like
  		//   return bytes.Equal(r.StartKey.Next(), r.EndKey)
  
  		startLen := len(r.StartKey)
  		return startLen+1 == len(r.EndKey) &&
  			r.EndKey[startLen] == 0 &&
  			bytes.Equal(r.StartKey, r.EndKey[:startLen])
  	}
  	// Works like
  	//   return bytes.Equal(r.StartKey.PrefixNext(), r.EndKey)
  
  	i := len(r.StartKey) - 1
  	for ; i >= 0; i-- {
  		if r.StartKey[i] != 255 {
  			break
  		}
  		if r.EndKey[i] != 0 {
  			return false
  		}
  	}
  	if i < 0 {
  		// In case all bytes in StartKey are 255.
  		return false
  	}
  	// The byte at diffIdx in StartKey should be one less than the byte at diffIdx in EndKey.
  	// And bytes in StartKey and EndKey before diffIdx should be equal.
  	diffOneIdx := i
  	return r.StartKey[diffOneIdx]+1 == r.EndKey[diffOneIdx] &&
  		bytes.Equal(r.StartKey[:diffOneIdx], r.EndKey[:diffOneIdx])
  }
docs: // IsPoint checks if the key range represents a point.