Constructs a DataCommand object.
string $selector: A CSS selector for the elements to which the data will be attached.
string $name: The key of the data to be attached to elements matched by the selector.
type $value: The value of the data to be attached to elements matched by the selector.
public function __construct($selector, $name, $value) {
$this->selector = $selector;
$this->name = $name;
$this->value = $value;
}