What is the datatype for the $config variable?

$config is a scalar (obviously) and contains a reference to a hash*. Hence when you dereference it, you use the arrow notation with curly braces around the hash key, eg: $config->{profile}->{Live}->{dat_file_location}

Unlike the DOM modules, XML::Simple sticks to the basic Perl data structures so the individual nodes are not objects and therefore have no methods.

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*There is an obscure condition in which XMLin() would return an array reference, but you're unlikely to happen across that by accident unless you generate your XML by passing XMLout an arrayref.