Document rules for 'contained' references

[pahjbo]

the code generation has relaxed the original strict VO-DML rules and allowed 'contained' references - i.e. the sorts of structures in lifecycleTest.vodsl. There still needs to be some rules imposed - e.g. if a reference is a contained reference - then it should not be be allowed also in a non-contained context

[pahjbo]

plugin 4.4 has a new schematron rule to warn about the lifecycle implications of contained references being used outside their containment hierarchy. This still needs to be documented though