The output you are showing looks like it was produced by Data::Dumper, yet the line print STDERR (Mojo::DOM->new($args->{$t})->at('iframe')); doesn't contain any references to Data::Dumper.
Could it be that you are confused, and the output is produced by some other code?
In reply to Re^3: how to extract iframes from text
by moritz
in thread how to extract iframes from text
by Anonymous Monk
| For: | Use: | ||
| & | & | ||
| < | < | ||
| > | > | ||
| [ | [ | ||
| ] | ] |