From eb22f82ed7c08d6378b65050a37f289a12b9959d Mon Sep 17 00:00:00 2001
From: Shunsuke Suzuki <suzuki.shunsuke.1989@gmail.com>
Date: Fri, 16 Oct 2020 08:08:22 +0900
Subject: [PATCH] docs: update README

---
 README.md | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/README.md b/README.md
index d9f581c..ac20185 100644
--- a/README.md
+++ b/README.md
@@ -364,6 +364,21 @@ ex.
 
 We can test external Tengo scripts with [suzuki-shunsuke/tengo-tester](https://github.com/suzuki-shunsuke/tengo-tester).
 
+## Restriction: map key should be string
+
+* meta
+* phase.meta
+* task.meta
+* task.items
+
+NG
+
+```yaml
+---
+meta:
+  true: foo # invalid key: key should be string
+```
+
 ## Configuration Reference
 
 ```yaml