diff --git a/docs/syntax.md b/docs/syntax.md
index 3523b8c..e36ca1f 100644
--- a/docs/syntax.md
+++ b/docs/syntax.md
@@ -217,6 +217,10 @@ abc
 **bold**
 ```
 
+```
+__bold__
+```
+
 ## ノード
 ```js
 {