Description:
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I don't know if this already has been reported or already supported, sorry if this is the case.

Test script:
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<?php
function canBeArrayOrString(string|array $route) {
  // Don't allow object, int, etc.!
}

Expected result:
----------------
Something like 'Must be string, array - object given!'

Actual result:
--------------
Valid when array or string has been given.