I have an xsd, where i define an element:
---el.xsd---
<schema version="1.0"
           xmlns="http://www.w3.org/2001/XMLSchema"
           xmlns:a="urn:attributes"
           targetNamespace="urn:elements"
           elementFormDefault="qualified">
    <import namespace="urn:attributes" schemaLocation="attr.xsd"/>
    <element name="el">
        <complexType>
            <attribute ref="a:attr"/>
        </complexType>
    </element>
</schema>

In an other namespace i define the 'attr' enumeration attribute.
---attr.xsd---
<schema version="1.0"
           xmlns="http://www.w3.org/2001/XMLSchema"
           targetNamespace="urn:attributes"
           attributeFormDefault="qualified">
    <attribute name="attr">
        <simpleType>
            <restriction base="string">
                <enumeration value="ONE"/>
                <enumeration value="TWO"/>
            </restriction>
        </simpleType>
    </attribute>
</schema>

Using theese schemas code completion can't list my enumeration.
<el
    xmlns="urn:elements"
    xmlns:a="urn:attributes"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:elements el.xsd" 
    a:attr="[CTRL_SPACE]"/>