vcs.ref.base.revision

base refers to the starting point of a change. For example, main would be the base reference of type branch if you've created a new reference of type branch from it and created new commits. The revision can be a full hash value (see glossary), of the recorded change to a ref within a repository pointing to a commit commit object. It does not necessarily have to be a hash; it can simply define a revision number which is an integer that is monotonically increasing. In cases where it is identical to the ref.base.name, it SHOULD still be included. It is up to the implementer to decide which value to set as the revision based on the VCS system and situational context.