diff --git a/protocol/src/main/java/com/zfoo/protocol/serializer/CodeTemplatePlaceholder.java b/protocol/src/main/java/com/zfoo/protocol/serializer/CodeTemplatePlaceholder.java
index 2fe82419..20308f91 100644
--- a/protocol/src/main/java/com/zfoo/protocol/serializer/CodeTemplatePlaceholder.java
+++ b/protocol/src/main/java/com/zfoo/protocol/serializer/CodeTemplatePlaceholder.java
@@ -67,6 +67,7 @@ public enum CodeTemplatePlaceholder {
                     .filter(it -> lineTrim.startsWith(it.placeholder))
                     .findAny();
             var formatLine = line;
+            // 形如 space ${protocol_class} 的占位符多了几个space，在生成代码的时候将每一行都添加相等的space，以此来对齐生成的多行代码块
             if (startPlaceholderOptional.isPresent()) {
                 var startPlaceholder = startPlaceholderOptional.get();
                 // calculate the tab length