#37 "ref" attribute support error

[Jędrzej Wasik]

Although documentation states "You can use ref attribute to refer element definition" (10.1.2), using it causes some errors connected with xs:list types.

ref seems to be working with simple xml structures.
I attached 4 files. Just run run.sh .
The code generates expection: "AttributeError: 'list' object has no attribute 'export'"
It works fine if i use type attribute instead of ref, but it generates huge limitations for .xsd formula.