Names the specific indexes in which an index term (<index-term>) should be used, for example, “author”, “subject”, “chemical”.
| Value | Meaning |
|---|---|
| A word or phrase | The name of the index, for example, “species”, “chemical”, “subject”, etc. |
| Restriction: | |
| Value | Meaning |
|---|---|
| One or more words | A word naming the index, or a series of words each representing a specific index |
| Restriction: | |