code: func (h *RequestHeader) HasAcceptEncodingBytes(acceptEncoding []byte) bool {
  	ae := h.peek(strAcceptEncoding)
  	n := bytes.Index(ae, acceptEncoding)
  	if n < 0 {
  		return false
  	}
  	b := ae[n+len(acceptEncoding):]
  	if len(b) > 0 && b[0] != ',' {
  		return false
  	}
  	if n == 0 {
  		return true
  	}
  	return ae[n-1] == ' '
  }
docs: // HasAcceptEncodingBytes returns true if the header contains
  // the given Accept-Encoding value.