Comma¶

Commas are syntax elements, to separate elements when provided as a list.

argument separator
parameter separator
trait name separator, in use expression
array element separator
list separator, where unused values may be omitted, leaving commas back to back.

They do not have a value by themselves.

<?php

function foo($a, $b) {
    return [$a, 2, $b];
}

list($y,, $z) = foo(1, 2);

?>