Complex attribute with Attribute and simpletype

[kanpeter]

Is it possible to combine the following into a single element (i.e.
SimpleType "FromTo" will be declared inside element "Frequency" and no
need to reference outside) ?

<xs:simpleType name="FromTo">
<xs:restriction base="xs:string">
<xsattern value="[0-9]?[0-9]?[0-9]|[0-9]?[0-9]?[0-9]-[0-9]?[0-9]?
[0-9]"/>
</xs:restriction>
</xs:simpleType>

<xs:element name="Frequency">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="FromTo">
<xs:attribute name="unit" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="Min."/>
<xs:enumeration value="Hr."/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>