The content from one of the linking services has been used to augment or replace content in the original citation.
This is an APA-specific (non-NLM) attribute.
| Value | Meaning |
|---|---|
| CR | CrossRef content was used. |
| PI | PsycINFO content was used. |
| PM | PubMed content was used. |
| Restriction: This attribute may be specified if the element is used. | |