1.4. Related documents
There are several other documents other than this Policy Manual that are necessary to fully understand some Debian policies and procedures.
The external “sub-policy” documents are referred to in:
In addition to those, which carry the weight of policy, there is the Debian Developer’s Reference. This document describes procedures and resources for Debian developers, but it is not normative; rather, it includes things that don’t belong in the Policy, such as best practices for developers.
The Developer’s Reference is available in the developers-reference package. It’s also available from the Debian web mirrors at https://www.debian.org/doc/developers-reference/.
Finally, a specification for machine-readable copyright files is maintained as part of the debian-policy package using the same procedure as the other policy documents. Use of this format is optional.