It's actually not covered later on in the evocation section or in the powers section. The quote you were using earlier is in reference to the specializations that full evocators receive, not focus items. Like I said originally it is only ever mentioned the once in the item crafting section, but now I'm just being argumentative. If you can't tell I'm a bit of a rules lawyer. I'm glad that everyone else has interpreted it in much the same way as I had long ago (before I looked at the specific wording).