Declaring jQuery Validate plugin rules -- attribute vs. class vs. code

In the examples for the jQuery Validate plugin, I see three different approaches to declaring validation rules:

• CSS Classes -- e.g. <input type="text" name="whatever" class="required" />
• Attributes -- e.g. <input type="text" name="whatever" required />
• JS code -- e.g. $("#myForm").validate({ rules: { whatever: "required", ... } });

But I don't see anywhere in the docs that explains why you'd use one over the other. Nor do I see an explanation of how to use the validation methods with each approach (for example, how would you use the "max( value )" method with a tag attribute or a css class?).

What are the tradeoffs between these three approaches? And how exactly do you declare all the different validation methods using each approach?