code: func (h *RequestHeader) SetBytesKV(key, value []byte) {
  	h.bufKV.key = append(h.bufKV.key[:0], key...)
  	normalizeHeaderKey(h.bufKV.key, h.disableNormalizing)
  	h.SetCanonical(h.bufKV.key, value)
  }
docs: // SetBytesKV sets the given 'key: value' header.
  //
  // Use AddBytesKV for setting multiple header values under the same key.