sed to specify the set of
        capabilities which can be used to build the bundle. While bundlecaps is
        unused in core Mercurial, extensions rely on this feature to communicate
        capabilities to customize the changegroup packer.

        shallow indicates whether shallow data might be sent. The packer may
        need to pack file contents not introduced by the changes being packed.

        fullnodes is the set of changelog nodes which should not be ellipsis
        nodes. We store this rather than the set of nodes that should be
        ellipsis because for very large histories we expect this to be
        significantly smaller.

        remote_sidedata is the set of sidedata categories wanted by the remote.
        Nc