フリー問題

問題文

A pattern must forbid a field from being present at all. Which anchor does this, and what value does the documentation recommend?

選択肢

1. The negation anchor, with the value set to the quoted word null.
2. The equality anchor, with the value set to an empty string in the pattern.
3. A plain field with the value null, because a pattern field whose value is null requires that the field not be defined and no anchor is therefore involved.
4. The existence anchor with an inverted value, because forbidding presence is the logical complement of requiring at least one occurrence and the same anchor covers both directions.