docs: mention usage of regexp literal in text expressions

[ignatiusmb]

Closes #5318

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[Conduitry]

Featuring this alongside other much more important and generally useful documentation still feels odd to me. As I mentioned in the original issue, I don't really have an answer where this should appear. I also don't know how many times this has come up in practice, or whether the original issue was @tanhauhau specifically looking for bugs.

[tanhauhau]

i raised the issue as a bug, but i'm not sure whether it should be documented as an intended behavior rather than fixing it

[Conduitry]

When this came up in the maintainers chat - https://discord.com/channels/457912077277855764/571775594002513921/749639227444297759 - pngwn and I talked about how it seems there's not really a reasonable way to handle this. If someone does {/if}/} then we can't tell whether this is a closing if tag or a regex.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[benmccann]

This doesn't seem like the worst place in the docs to put it, but I'd probably put it in an aside box instead of the main text

[benmccann]

Suggested change

	However, if you're using a regular expression (`RegExp`) [literal notation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp#literal_notation_and_constructor), you'll need to wrap it in parentheses.
	> If you're using a regular expression (`RegExp`) [literal notation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp#literal_notation_and_constructor), you'll need to wrap it in parentheses.

[ignatiusmb]

Placing it in an aside box seems nice. I haven't seen what it'll look like on the page if we do that, but I see in the current docs that blockquotes are always placed after a main text first. Should we also remove the separator above? What about the example code after it?

[benmccann]

This blue box is an example: https://svelte.dev/docs#get

Yes, I think we could remove the separator in that case. Can we put the code example in the box? (maybe if you prefix each line with > it will do that. you can test by running the site locally, which I think is cd site; npm install; npm run update; npm run dev)

[ignatiusmb]

It looks a bit weird

[ignatiusmb]

I've changed and merged it to the previous row, I think this is clearer and follows the style (like https://svelte.dev/docs#get) better