code: func (h *RequestHeader) SetByteRange(startPos, endPos int) {
  	h.parseRawHeaders()
  
  	b := h.bufKV.value[:0]
  	b = append(b, strBytes...)
  	b = append(b, '=')
  	if startPos >= 0 {
  		b = AppendUint(b, startPos)
  	} else {
  		endPos = -startPos
  	}
  	b = append(b, '-')
  	if endPos >= 0 {
  		b = AppendUint(b, endPos)
  	}
  	h.bufKV.value = b
  
  	h.SetCanonical(strRange, h.bufKV.value)
  }
docs: // SetByteRange sets 'Range: bytes=startPos-endPos' header.
  //
  //     * If startPos is negative, then 'bytes=-startPos' value is set.
  //     * If endPos is negative, then 'bytes=startPos-' value is set.