resolved jelly namespace URIs to embedded XSDs to support syntax completion

The error-marked jelly namespace URI's and code completion issue is caused by Intellij not handling jar: URL schemes in its ExternalResourceManager. My solution was to mangle the URL external form to strip the jar: and file: prefixes and un-escape the file path part (which contains %20s when executed on a Mac) in a platform-independent way by following the procedure described here:

https://weblogs.java.net/blog/kohsuke/archive/2007/04/how_to_convert.html