dst.WriteString(`u00`)
				dst.WriteByte(hexTable[b>>4])
				dst.WriteByte(hexTable[b&0xF])
			}
			i++
			start = i
			continue
		}
		c, size := utf8.DecodeRuneInString(s[i:])
		if c == utf8.RuneError && size == 1 {
			if start < i {
				dst.WriteString(s[start:i])
			}
			dst.WriteString(`\ufffd`)
			i += size
			start = i
			continue
		}
		// U+2028 is LINE SEPARATOR.