How to interpret E:enabled:first-of-type

In CSS3 Selectors, I can see two possible interpretations of
E:enabled:first-of-type.

One is that it returns the first enabled element of type E. That is, this
selects the first child that matches E:enabled.

The second is that it returns the first child of type E provided that it
is enabled.

I don't see anything in the specification that would prefer one over the
other altho, If the first is the correct interpretation, then I can get the
effect of the second in this case with the selector E:first-of-type:enabled.
If the second is the correct interpretion, I can't see anyway to get the
effect of the first interpretation.

Can anyone shed light over what should happen and/or what does happen if
there is a browser that implements this yet?