If you happen to get an error “External resource http://example.com/example.xsd is not registered” when validating an XML file in PphStorm, check, if the URI of your
noNamespaceSchemaLocation is marked red. If so, this schema is simply not loaded.
Click in the line with your schema declaration und hit
<ALT><ENTER>, choose “Fetch external resource” to load this resource. The URI of your
noNamespaceSchemaLocation should be marked green now and your document can be validated.