It's nice to have.
I think this would be a great improvement.
I prefer this:
$result = "Hello World" |> htmlentities(...) |> str_split(...) |> fn($x) => array_map(strtoupper(...), $x) |> fn($x) => array_filter($x, fn($v) => $v != 'O');
instead of this:
$result = "Hello World" |> 'htmlentities' |> 'str_split' |> fn($x) => array_map('strtoupper', $x) |> fn($x) => array_filter($x, fn($v) => $v != 'O');