I added your example to the concept map. It is a good another example of array of arrays. Also, I wrote and added this lines to the section 'HASH OF HASHES WITH LISTS OF VALUES'

push @{$ref->{'key1'}->{'key2'}}, "@{$adds}"; 
      # anonymous array: $adds = ["e","f"];
print "@{$ref->{'key2'}->{'key'}}"; # output: c d e f
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I found useful 'perldoc perl...', till time I was searching for any info in the Internet.