I have the following JSON-encoded string:

```
$json = '"|\t|\n|\\\u0027|\\\u0022|"';

```

What is the most efficient way to **escape *all* the (already) escaped chars / codepoints except `\\\u0022` or `\\\u0027`?** I though about using `preg_replace()` with a negative lookahead regular expression but it's not working as I expected, the output should be:

```
$json = '"|\\\t|\\\n|\\\u0027|\\\u0022|"';

```

I'm feeling lost in this ocean of JSON-PHP-PCRE escaping, can someone help me out?