My thanks Martti for help on my original question.
In my haste, I oversimplified the real problem.
What I really want is a general rule such that:
- Warnings are optional, but if there are any, they must be first.
- Cautions are optional, but if there are any, they must be after warnings (if any). i.e. gen. rule: warning*, caution*
- Notes and paras are optional, there can be multiples of each, and they can be in any order after the warnings and cautions.
- At least one of the elements must be present.
Valid: warning
Valid: caution
Valid: note
Valid: para
Valid: warning1, warning 2, caution, note, para, note
Not valid: warning1, caution, note, warning2
Not valid: para, caution
Thanks again for the help.
Joan