Now that we have a syntax that lets you both specify a CSS property that will style an attribute and at the same time specify a default value for that attribute,
[E.g.: <attribute name="bgcolor" type="color" style="background-color" value="pink" /> specifies that you can use CSS to change bgcolor to blue by specifying `background-color: blue` in a <stylesheet>, but that in the absence of any applicable style rule, the bgcolor will be pink.] I think we should _require_ that you specify a default value for such attributes, and that that default value must be a valid value for the declared type. Is there any reason you would ever _not_ want a default value?
