"my" "dog"            <-- valid
"my" "dog shepherd"   <-- valid
my dog                <-- valid
my "dog shepherd"     <-- valid
"my "dog"             <-- invalid
my "dog shepherd      <-- invalid

##</code><code>##

 
$in =~ /(["]?)[^" ]+\$&\s+ (["]?)[^" ]+\$&/