1./test/relaxng/tutor6_2_4.xml:4: element preferredFormat: Relax-NG validity error : Error validating value
2./test/relaxng/tutor6_2_4.xml:4: element preferredFormat: Relax-NG validity error : Element preferredFormat failed to validate content
3./test/relaxng/tutor6_2_4.xml fails to validate
4