The fundamental point is that a reference is just another kind of scalar value. Anywhere you can put 3 or "ouch", you can put a reference. So an arrayref need not be the simple scalar variable in the example ($aref), it could be an element of an array ($refs[9]) or the value of a hash element ($hits{"blue"}).

So, given that $data{$query} contains an array ref, you can push things on that array via

    push @{ $data{$query} }, $thing;
[download]

To return a hash by reference, you treat the hash variable as an opaque container. Like so:

    return \%data;
[download]