Clarification on Action element

In section 2.7.4.2 of core spec, Namespace is marked as "Optional". It says:
"If this element is absent, the namespace
urn:oasis:names:tx:SAML:1.0:action:rwedc-negation specified in Section
8.1.2 is in effect."

But in the following schema definition, attribute Namespace is marked as
required:
<attribute name="Namespace" type="anyURI" use="required"/>

Anyone knows what is the intent here? Does it mean <Action> element must
have an attribute called Namespace, but the value of this attribute
could be empty, like this?

<Action Namespace="">Read</Action>

Thanks,
Emily