In #9888, it was reported that my earlier pull request #9075 didn't quite function as expected. I was quite hopeful the `ValuesWithShadow()` worked as expected (and, I thought my testing showed it did) but I guess not. @zeripath proposed an alternative syntax which I like:
```ini
[markup.sanitizer.1]
ELEMENT=a
ALLOW_ATTR=target
REGEXP=something
[markup.sanitizer.2]
ELEMENT=a
ALLOW_ATTR=target
REGEXP=something
```
This was quite easy to adopt into the existing code. I've done so in a semi-backwards-compatible manner:
- The value from `.Value()` is used for each element.
- We parse `[markup.sanitizer]` and all `[markup.sanitizer.*]` sections and add them as rules.
This means that existing configs will load one rule (not all rules). It also means people can use string identifiers (`[markup.sanitiser.KaTeX]`) if they prefer, instead of numbered ones.
Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>
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