what does a comma do in the first parameter of a for loop?

Question

What does it mean when there is a comma in the first parameter of a for loop?

For example:

for ($j=0, $n2=sizeof($quotes[$i]['methods']); $j<$n2; $j++) {
    //
}

Answer 1

A comma in the first section of the loop just separates variable declarations.

Essentially it is just declaring two variables $j=0 and $n2=sizeof($quotes[$i]['methods']), but in the loop constructor instead of before the loop constructor.