Safe #schedule. Schedules this form for opening (aka execution or evaluation) in engine, or opens it immediately (see ShouldOpenWhenScheduled).

See Engine to learn about the difference between #schedule, on_open, and on_parent_open.

Unsafe #schedule. Use #schedule unless you have instantiated this form yourself, or know what you're doing.

Override this if you want to implement both safe #schedule and unsafe #schedule! for your form type: safe #schedule simply delegates to #schedule! unless it is explicitly overridden.

By default, simply pushes this form onto stack.