| Attachment | 0..* | — | Content in a format defined elsewhere |
| .id | 0..1 | String | Unique id for inter-element referencing |
| .extension | 0..* | Extension | Additional content defined by implementations |
| .contentTypeΣ | 0..1 | code | Mime type of the content, with charset etc. |
| .languageΣ | 0..1 | code | Human language of the content (BCP-47) |
| .data | 0..1 | base64Binary | Data inline, base64ed |
| .urlΣ | 0..1 | url | Uri where the data can be found |
| .sizeΣ | 0..1 | unsignedInt | Number of bytes of content (if url provided) |
| .hashΣ | 0..1 | base64Binary | Hash of the data (sha-1, base64ed) |
| .titleΣ | 0..1 | string | Label to display in place of the data |
| .creationΣ | 0..1 | dateTime | Date attachment was first created |