I think it's part of the "call setters" in the life cycle. The specification does not clearly mention if it is before or after calling the setters of declared attributes. So I guess it does not matter whether it's before or after, as long as the dynamic attributes are set properly.
Actually, there's an example in the spec showing an order of call :
In the following example, assume attributes a and b are declared using the attribute element in the TLD, attributes d1 and d2 are not declared, and the dynamicattributes element is set to �true�. The attributes are set using the calls:
So, in the life cycle, this is part of : 3. The setters for each attribute defined for this tag are called by the container.