javascript dom, how to handle "special properties" as versus attributes?

issue is whether to use property or attribute.

have not found this documented, so have run some tests (chromium 12):

property <=> attribute

accept, alt, formMethod, formTarget, id, name, placeholder, type, maxlength, size
form: method, name, target, action, enctype

• can set either property or attribute
• will reflect to property or attribute
• exception 1: if form property will first look for element of that name (!)
• exception 2: action property rewrites itself using value, passes set value to attribute
• exception 3: enctype maintains its integrity, but passes set value to attribute

property <= attribute

value, autofocus, checked, disabled, formNoValidate, multiple, required

• setting property has no effect on attribute
• setting attribute also sets property

property => attribute

indeterminate

• setting property also sets attribute
• setting attribute has no effect on property

propetry >< attribute

defaultValue, validity, defaultChecked, readOnly
form: novalidate

• setting property or attribute has no effect on the other

given a random attribute/value to apply to an element, here are the best rules I have come up with (modified as per Tim Down (thanks!) below):

• if class, write with classList, read with className property

• if a form, always read using attribute (and be a little careful)

• if typeof element[propName] != "undefined", use property, ie, element[attr]=val

• otherwise, use attribute, ie, element.setAttribute(attr,val)

is this even close to b