PP8: Illustration of
- composite states
- 'return to history' (via transition 'timeout2' in 'Client'),
- 'unexpected messages' (due to 'Interrupt' state in 'Client')
To try:
- set 'INTERRUPTS_ENABED' to 'true'
- add transition t from 'Interupt' to 'Error' with unexpected 'result' as trigger
- make t untakable by adding guard 'false'

PP9: Illustration of data classes and messages with more than one parameter
- class 'Args' packages all parameters for messing 'init' from 'Top' to 'Pinger'
- in 'Top' and 'Pinger', set dependency to class 'Args' with 'Kind In Header' set to 'none' and 'Kind in Implementation' set to 'inclusion'

PP10: Illustration of defer/recall using PP8