Well, $$ returns a collection, any Element operation you execute on that
collection returns an array rather than a single value.
For example:
$$('div') - returns all divs as array [div, div]
$$('div').getStyle('width') - returns the width of all divs in an array
['10px', '5px']
$$('div').getChildren() - returns the children of the divs as array of
arrays [[p, p], [p, span]]
Similar, $$('div').getFirst() returns an array containing the first child of
every div: - [p, span]
$$('div > *') - returns the children of all divs in one array [p, p, p,
span]
$$('div').getChildren().flatten() basically equals $$('div > *')
