3) In this syntax $1 = ((.*)EDITION\/|Edition\/) and $2 = (.*), so what will be $3 ?

A numbered capture group is numbered according to the strict order in which its opening parenthesis appears in the regex:
   $1 --+-----------------------+
        |                       |
        V                       V
       /((.*)EDITION\/|Edition\/)(.*)/
         ^  ^                    ^  ^
         |  |                    |  |
    $2 --+--+               $3 --+--+
See perlre, and also Grouping things and hierarchical matching and Extracting matches in perlretut.