PHP uses function to define functions, which is consistent with js.
The keyword parameter (default parameter) is placed at the end, and no value is required.
Regarding scope, note that external variables cannot be used in the function body. (This curious flower)
PHP supports two ways of multi-value parameter passing (the second one needs to correspond to the type parameter)
PHP supports anonymous function operations (can be referenced by a variable)
Some built-in functions of php:
