The plan · The slots · Element
The slot
What goes out and when.
The part
What it is
Format, channel, subject and date. Enough to be actionable and no more, since detail at planning stage is usually discarded.
Linked to the job it serves, so that a slot filled with something convenient is visible as a substitution.
The smallest level
The attributes it carries
Each attribute is one of the framework’s shared types. What a date is, and how it is written, is defined once for the whole model — the note here says what it means in this particular place.