An HTML content command for setting or removing the "checked" attribute on an HTML element.
The value of this command's primary attribute is interpreted as a Boolean value. If the value resolves into true, the "checked" attribute is set. Otherwise the attribute is not set, or removed if the host element currently has it.
This command has a priority of 15.
checked command doesn't do much in other elements besides
input elements of the type "checkbox". If its primary attribute resolves into
true, the checkbox will appear as checked, otherwise not.
<input name="checked" type="checkbox" dyn-checked="initiallyChecked"/>