fix comments

compress.go

@@ -15,7 +15,8 @@ type NodeImporter interface {
 
 // CompressExporter wraps the normal exporter to apply some compressions on `ExportNode`:
 // - branch keys are skipped
-// - leaf keys are encoded with delta-encoding
+// - leaf keys are encoded with delta compared with the previous leaf
+// - branch node's version are encoded with delta compared with the max version in it's children
 type CompressExporter struct {
 	inner        NodeExporter
 	lastKey      []byte
@@ -53,8 +54,7 @@ func (e *CompressExporter) Next() (*ExportNode, error) {
 	return n, nil
 }
 
-// CompressImporter wraps the normal importer to do de-compressions before hand,
-// NOTE: it don't need to re-fill the branch keys, because the import logic can handle that directly.
+// CompressImporter wraps the normal importer to do de-compressions before hand.
 type CompressImporter struct {
 	inner        NodeImporter
 	lastKey      []byte