Enable syntax fold on multiline backtick strings

[guyzmo]

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Hello, I've been using a lot multiline backtick strings and I'd like to enable folds on them.

I've been trying to set something like, adding fold to the backtick syntax:

syntax region tsxString fold contained start=+`+ end=+`+ contains=tsxEntity,@Spell display

But with no success yet. Though, I've never tweaked folds in a syntax before.