diff --git a/system-variables.md b/system-variables.md
index 7324eaafabc60..c6083a3e9411a 100644
--- a/system-variables.md
+++ b/system-variables.md
@@ -535,9 +535,9 @@ Constraint checking is always performed in place for pessimistic transactions (d
     * `LOCK IN SHARE MODE` syntax
     * `SQL_CALC_FOUND_ROWS` syntax
 
-> **Note:**
+> **Warning:**
 >
-> Only the default value of `OFF` can be considered safe. Setting `tidb_enable_noop_functions=1` might lead to unexpected behaviors in your application, because it permits TiDB to ignore certain syntax without providing an error.
+> Only the default value of `OFF` can be considered safe. Setting `tidb_enable_noop_functions=1` might lead to unexpected behaviors in your application, because it permits TiDB to ignore certain syntax without providing an error. For example, the syntax `START TRANSACTION READ ONLY` is permitted, but the transaction remains in read-write mode.
 
 ### tidb_enable_parallel_apply <span class="version-mark">New in v5.0</span>