code: func AppendQuotedArg(dst, src []byte) []byte {
  	for _, c := range src {
  		// See http://www.w3.org/TR/html5/forms.html#form-submission-algorithm
  		if c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z' || c >= '0' && c <= '9' ||
  			c == '*' || c == '-' || c == '.' || c == '_' {
  			dst = append(dst, c)
  		} else {
  			dst = append(dst, '%', hexCharUpper(c>>4), hexCharUpper(c&15))
  		}
  	}
  	return dst
  }
docs: // AppendQuotedArg appends url-encoded src to dst and returns appended dst.