// escapeStringJSON will escape a string for JSON and write it to dst.
func escapeStringJSON(dst *bytes.Buffer, s string) {
	start := 0
	for i := 0; i < len(s); {
		if b := s[i]; b < utf8.RuneSelf {
			if htmlSafeSet[b] {
				i++
				continue
			}
			if start < i {
				dst.WriteString(s[start:i])
			}
			dst.WriteByte('\\')
			switch b {
			case '\\', '"':
				dst.WriteByte(b)
			case '\n':