$ jing greeting.rng greeting3.xml /Users/elharo/Documents/speaking/sd2005west/relaxng/examples/greeting3.xml: 3:6: error: unknown element "P"
Notice how completely decoupled the validation is from the instance document. We can validate any document against any schema. We do not need to specify the schema in the instance document as you must do with DTDs and often need to do with W3C schemas.