List itemTypes

In XML-Schema Part 2:

2.5.1.2 List datatypes
...
[Definition:]   The ·atomic· datatype that participates in the definition of
a ·list· datatype is known as the itemType of that ·list· datatype.
...


Later on, in the same document:
4.1.2.2 Derivation by list
...
A ·list· datatype must be ·derived· from an ·atomic· or a ·union· datatype,
known as the ·itemType· of the ·list· datatype.
...


The two statements are contradicting. Could you please clarify if the
itemType of a list is meant to be
of "atomic" type ONLY or
of EITHER "atomic" OR "union" type?

Thanks,
Panagiotis