code: func unescapeToUTF8(in, out []byte) (inLen int, outLen int) {
  	if len(in) < 2 || in[0] != '\\' {
  		// Invalid escape due to insufficient characters for any escape or no initial backslash
  		return -1, -1
  	}
  
  	// https://tools.ietf.org/html/rfc7159#section-7
  	switch e := in[1]; e {
  	case '"', '\\', '/', 'b', 'f', 'n', 'r', 't':
  		// Valid basic 2-character escapes (use lookup table)
  		out[0] = backslashCharEscapeTable[e]
  		return 2, 1
  	case 'u':
  		// Unicode escape
  		if r, inLen := decodeUnicodeEscape(in); inLen == -1 {
  			// Invalid Unicode escape
  			return -1, -1
  		} else {
  			// Valid Unicode escape; re-encode as UTF8
  			outLen := utf8.EncodeRune(out, r)
  			return inLen, outLen
  		}
  	}
  
  	return -1, -1
  }
docs: // unescapeToUTF8 unescapes the single escape sequence starting at 'in' into 'out' and returns
  // how many characters were consumed from 'in' and emitted into 'out'.
  // If a valid escape sequence does not appear as a prefix of 'in', (-1, -1) to signal the error.