Better use escapes here to make it easier on our eyes.

You can write `U+0009` as `"\x{0009}"` in Elixir.

I would also add a test for all metachars and some common whitespace, as a sanitiy check:

```
string = "\\A.^$*+?()[{\\| \t\n\xff\\z #hello\x{202F}\x{205F}"
assert string =~ %r/#{Regex.escape(string)}/usimx
```