Builtins and runtime

Calling builtins, control-flow idioms, how scripts run, errors, the language's limits, the Steps engine and common gotchas.

• Calling builtins — How builtin arguments are checked, what builtins return, and how plural results are enumerated.
• Control-flow idioms — The standard substitutes for while, break, continue, modulo, the ternary operator and reusable functions.
• How scripts run — Threads, blocking, stopping, what persists between runs, scripts passed as Text, trigger context, snippets and Safe Mode.
• Serial devices and Arduino — Connecting Arduino boards and other COM-port devices: finding the port, speeds and line endings, one-off exchanges, a port kept open, and monitors that react to every line.
• Errors — Compile errors, builtin failures and soft results, and the common compile errors with their fixes.
• What the language doesn't have — The features the language leaves out on purpose, and the workaround for each.
• The Steps engine — How a Steps action's TOML list of steps differs from a Script action.
• Gotchas — Expressions that don't do what they look like they do, and why.