Two schema validation modes?

I've always thought that we did schema validation in two different
ways in XForms:
1) value validation during xforms-revalidate (instance node changes, etc.)
2) full schema validation before submission

Much to my suprise I cannot find wording for that in the
specification. Am I blind, or is it just something that we have only
talked about (or both :) )?

-- 
... Allan