Identifies which version of the DTD, named in the DOCTYPE declaration, was used to make the book (or book collection) under consideration, which therefore can be used to validate this book (or book collection)
Authoring Note: This is a “fixed” attribute (meaning that the value is set via a Parameter Entity in the DTD; thus, an author or editor cannot change it) that should change every time the DTD changes versions or revisions.
| Value | Meaning |
|---|---|
| 2.0 | The 2.0 version of the NCBI Book DTD (or NCBI Collection DTD) is being used. |
| Restriction: This attribute value may not be changed. | |