Right now the XML plugin works only with XML schema 1.0. In particular, it is possible to edit a user-defined XSD file using XML Schema 1.0 (XMLschema.xsd for version 1.0 from https://www.w3.org/2001/XMLSchema.html).
An attempt to use XML Schema 1.1 (XMLschema.xsd for version 1.1 from the same location) triggers multiple errors.
Most errors are in the form:
...:s4s-att-not-allowed: Attribute '...' cannot appear in element '...'.
And there are a couple of other errors.
In total, the plugin reports 101 errors when trying to use http://www.w3.org/2009/XMLSchema/XMLSchema.xsd (XML schema 1.1) instead of http://www.w3.org/2001/XMLSchema.xsd (XML schema 1.0)
To reproduce:
test.xsd
in jEdit.schemas0.xml
to schemas.xml
.