The three dots in trim(...) make a callable out of a function, that was already in, so seem best to re-use that syntax, at least for now. [1]

As for the partial function application, there is already an RFC to add that, but it's not decided on as of now. [2]

1: https://www.php.net/manual/en/functions.first_class_callable...

2: https://wiki.php.net/rfc/partial_function_application_v2