Nested hashes and arrays could be forced into all three, albeit perhaps at the expense of some awkwardness. After all, it's all structured data. Below is just a quick example and I'm not writing this node to promote writing code to support this data structure. It's certainly not impossible, though, to denote these things.:

my %data = (
    'attributes' => {
        '_name' => 'mydata',
        'height' => 50,
        'width'  => '80%',
    },
    'children' => [
        { 'attributes' => { '_name' => 'bob', ...} ...},
        { 'attributes' => { '_name' => 'tom', ...} ...},
    ],
    'content' => 'yadda yadda ...',
);
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Whether that's something you'd want to process later is another issue. Some people like to put a lot of predetermined information about their data into their code. Others like to keep the data as self-describing as possible and keep the code very general to work with that. There are strengths and weaknesses to either approach.