Type of source identifier (for example, a DOI, ISSN, ISBN, or publisher’s identifier) for a <related-object>.
| Value | Meaning |
|---|---|
| The type of identifier that names the source of the related object, for example, a DOI. | The type of document identifier named in the @source-id attribute for a (<related-object>) element. This attribute qualifies the @source-id attribute. |
| Text, numbers, or special characters | |
| Restriction: | |