/"((?:[^"]+(?=")|"")*)"(?!")/
#          ^^^^^

##</code><code>##

/"((?:(?>[^"]+)|"")*)"(?!")/
#     ^^^     ^

##</code><code>##

if(  /"((?:[^"]+|"")*)("?)(?!")/  ) {
#                     ^ ^^
    die "Unclosed quote ($1)..." if ! $2;