What's the A template?

As documented in pack, it's a "text (ASCII) string, will be space padded." I showed the differences between some of those pack templates here.

Can you say a few words about this line of code (I've never seen this before in Data::Dumper)? print Data::Dumper->Dumpxs( [ $raRect ], [ qw{ raRect } ] );

Simplifying a lot, Dumpxs is just another name for Dump. (See Where is Data::Dumper->Dumpx?)