The duration

How long the test runs.

The part

What it is

Longer than the sales cycle, or the test measures the pipeline rather than demand. For long cycles this makes holdouts expensive and still worth doing.

Ending early because the result looks clear is the most common way a holdout is invalidated.

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.