<?phpfunction add_some_extra(&$string){ $string .= 'and something extra.';}$str = 'This is a string, ';add_some_extra($str);echo $str; // outputs 'This is a string, and something extra.'?>

The given code is written in PHP. It defines a function add_some_extra that takes a reference to a string and appends the text 'and something extra.' to it.

Here's a step-by-step explanation:

1. The function add_some_extra is defined. It takes one parameter, $string, which is passed by reference. This means that any changes made to $string inside the function will affect the original variable that was passed in.

2. A string $str is defined with the value 'This is a string, '.

3. The function add_some_extra is called with $str as the argument. Inside the function, the text 'and something extra.' is appended to $str.

4. The echo statement prints the value of $str, which is now 'This is a string, and something extra.' because the function modified the original $str variable.

So, the output of this PHP code will be: 'This is a string, and something extra.'