Improve readability of annotation syntaxes about luals.github.io HOT 3 OPEN

Maybe using colors to differentiate between placeholders and real syntax?
It doesn't have to just be colors, a hover card describing possible example values could also help.

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My initial thought was to use colours, but there could be issues then with colourblind users. I think I'll give it a try using iWantHue and see how it looks.

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I'm not really sure whether this is better 😆

It might just be slightly easier to read than the current definition:

I can try adding a colour specifically for the repeatable brackets… maybe that will help in the case of @cast.

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