Question: I want a RegEx to match any Hex number but `7E` and `7D`.

To match any Hex number I use `[0-9A-F]{2}`. How can I now exclude the unwandted numbers?

Answer: 
You could use a negative look-ahead that would fail on `7E` or `7D`. The following pattern uses `^` and `$` to match the entire string, not a partial match within a string.

```
^(?!7[ED])[0-9A-F]{2}$

```
You could use something like this:

`[0-68-F][0-F] || 7[0-CF]`

(the `||` might not work, depending on where you're using this regex. You didn't specify that in your question)