The editor enhances the content completion of the XML editor inside the xs:annotation/xs:appinfo elements of an XML Schema with special support for the elements and attributes from a custom schema (by default ISO Schematron). This content completion enhancement can be configured from the XSD Content Completion preferences page.
If the current XML Schema schema imports or includes other XML Schema schemas then the global types and elements defined in the imported / included schemas are available in the content completion window together with the ones defined in the current file.
Schematron Support in XML Schema Content Completion