You don't need to predefine your datastructure as it will be created as you insert the data, which you could do like so

my %tagstack;
# ... parsing code here
push @{$tagstack{requirements}}, {
    # $tag = wherever the data is coming from
    text       => $tag{cdata},
    attributes => $tag{attribs}
};
[download]

If you're just using simple nested hashes then XML::Simple may be just the module for you, and if you continue to get muddled by references and reference syntax check out the perlreftut and perlref manpages.
HTH

_________
broquaint