Over the weekend I used Carl Mäsak's SVG module (Perl 6), which -- despite its name -- is general XML serializer.

It uses Pair objects for both attributes and child tags, distinguished by the type of the value: if the value is an List, it's used as a child tag, if it's a scalar it's used as an attribute.

The documentation uses this example:

my $svg = :svg[             # root tag
    :width(200),            # attribute
    :height(200),           #
    circle => [             # child tag
        :cx(100), :cy(100), :r(50)      # child tag attributes
    ],
    text => [               # child tag
        :x(10), :y(20), "hello"         # child tag attributes
    ]
];
[download]

I used this data structure to generate bar charts in SVG, and found it very handy.