private void populateDiffStrings(ClusterStateBundle state, ClusterStateBundle prevState) {
        // Yes, it's correct to get the diff by doing old.getHtmlDifference(new) rather than the other way around.
        diffs.put(BASELINE, prevState.getBaselineClusterState().getHtmlDifference(state.getBaselineClusterState()));
        var spaceDiffs = state.getDerivedBucketSpaceStates().entrySet().stream()
                .collect(Collectors.toMap(
                        entry -> entry.getKey(),
                        entry -> derivedStateOf(prevState, entry.getKey()).getHtmlDifference(entry.getValue().getClusterState())));
        diffs.putAll(spaceDiffs);
    }
Represents the absolute cluster states (baseline + derived) for a given version
as well as the relative diffs (baseline + derived) since the previous version.
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/ClusterStateHistoryEntry.java