->jing aet.rng aet.xml
/tmp/aet.xml:5:35: error: unfinished element
/tmp/aet.xml:6:55: error: element "engineType" not allowed in this context

->xmllint --noout --relaxng aet.rng aet.xml
aet.xml:5: element automobile: Relax-NG validity error : Element automobile failed to validate attributes
aet.xml:5: element automobile: Relax-NG validity error : Expecting an element engineType, got nothing
aet.xml:5: element automobile: Relax-NG validity error : Element automobile failed to validate content
aet.xml:4: element automobile: Relax-NG validity error : Element cars has extra content: automobile
aet.xml fails to validate

->java -jar jing.jar aet.sch aet.xml
/tmp/aet.xml:5: error: assertion failed:
  Engine type must be specified. You have your choice of an attribute or child element
/tmp/aet.xml:6: error: report:
  Engine type can not be specified twice.