Error in Counter interface

The Counter interface of the DOM Spec states:
" The Counter interface is used to represent any counter or counters
function value. This interface reflects the values in the underlying style
property. Hence, modifications made to the
CSSPrimitiveValue [p.149] objects modify the style property. "

However the interface only has DOMString attributes.  Shouldn't all of
these attributes CSSPrimitiveValue's instead?

Thanks,

Blaine Brodie