What is the deprecation message for the usort() function regarding returning a boolean from the comparison function, and what should be returned instead?

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The deprecation message for the usort() function regarding returning a boolean from the comparison function is "Returning bool values from comparison functions is deprecated. Return an integer less than, equal to, or greater than zero". Instead of returning a boolean, the comparison function should return an integer, either less than, equal to, or greater than zero, indicating the order of the two elements being compared.