<!-- TMPL_LOOP NAME=loop1 -->
# means you must have a hash key 'loop1' with an array ref as its value
# in the hash.

%loop_data = ( loop1 => [ ..something.. ] );


<!-- TMPL_LOOP NAME=loop2 -->
# another loop, so each of these 'somethings' must have a hash key loop2
# pointing to a value of some array ref

%loop_data = ( loop1 => [ { loop2 => [ ..something.. ] },
                          { loop2 => [ ..something.. ] },
                          ...
                        ]
             );

<!-- TMPL_VAR NAME=var1 -->
# now each of these somethings must contain a hash key var1 pointing to
# some scalar data.

%loop_data = ( loop1 => [ { loop2 => [ { var1 => 'data'} ] },
                          { loop2 => [ { var1 => 'otherdata'} ] },
                          ...
                        ]
             );