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\ characters to nest placeholders. You simply need to have a hierarchy of square brackets. For example, if you start with a quotation mark “ and want to place a placeholder argument inside it, you must use the other type of quotation mark ', and if another argument is required inside that argument, it must be interspersed with the other type of quotation mark ”. The wiki explains this better and provides examples.
Add MiniPlaceholders placeholders for complex mathematical and text expressions