Reference appendix

The appendix collects the facts the other parts refer to, to look up rather than read through:

1. Statuses: the statuses of process runs, nodes, trigger runs and agents.
2. Validation rules: every message the designer's check can give, with the chapter that explains it.
3. Expression functions: every function you can use in an expression, with examples.
4. Glossary: the words this guide uses, and where each is explained.