A list validation IS a vocabulary, and frequently the only place a sheet states one: what
Region is allowed to contain is exactly what a writer needs before writing, and what a reader
needs to recognize ZZ as wrong rather than as new. The rule text reports a picked set as a
count (Any of 3 Items) because a filter dropdown cannot show a hundred values, so a report
that only carried the rule left the vocabulary unreadable.
A list sourced from cells carries its formula instead of its values — that IS the answer, and it is the address to read next.
The values a list validation admits, spelled out — or the formula the list is read from.