A BOM is a dry description of the product or approach. Performance characteristics if you want. Documentation may include advice on the use of the product based on the specifications, or Vice versa the Council not use.
The link that You gave is the API specification JDK 8.
When developing I use mainly Google, to find documentation. To the specification used in extremely complicated cases, such as when we make our API implementation of something, and we need to adhere to the specifications.
The Java language specification is at the following address: https://docs.oracle.com/javase/specs/
IMHO, to understand it-not even those who wrote it)