If the schema includes itself or through the another schema, Idea highlights the errors on some elements, as not defined in this schema.
Example:

<xs:element name="userrole">
<xs:complexType mixed="true">
<xs:sequence minOccurs="0">
<xs:any namespace="http://www.w3.org/1999/xhtml ##targetNamespace" minOccurs="0" maxOccurs="unbounded"></xs:any>
</xs:sequence>
</xs:complexType>
</xs:element>

<xs:element name="label">
<xs:complexType>
<xs:attribute name="key" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:whiteSpace value="collapse"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType
</xs:element>

It's impossible to use the "label" element inside of the "userrole" element though it's defined by the schema. Oxygen XML Editor and Xalan XML Parser accepts this combination as valid, so I except the IntelliJ will do the same.

Can you release a quick fix for us, please? It's critical for our projet. We have to use now the external tools to edit our xml files.

Environment: WinXP

Issue was resolved