From 43db9630a42c5d1dc0e1b41c45bfa0c02a53803c Mon Sep 17 00:00:00 2001
From: Nicco <hi@nicco.io>
Date: Sat, 19 Oct 2019 20:15:18 +0200
Subject: [PATCH] Update README.md

---
 README.md | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 83ddd9b..83a9a1c 100644
--- a/README.md
+++ b/README.md
@@ -188,7 +188,9 @@ const initial = {
 
 ### Validators
 
-A validator is an object that taked in either a `RegExp` or a `Function` (can be async). Optionally you can pass a message string that will be displayed instead of the default one.
+A validator is an object that taked in either a `RegExp` or a `Function` (can be async) or an array of those. Optionally you can pass a message string that will be displayed instead of the default one.
+
+A validator functions takes the current value as input and should return a `boolean` or a `string`. If returned `true` the input counts as valid, if `false` it's not. If you pass a string formhero will treat it as not valid and display the string returned as error message.
 
 ###### Example: Regular Expression
 
@@ -238,6 +240,17 @@ const validators = {
 }
 ```
 
+###### Example: Dynamic Error Message
+
+```javascript
+const validators = {
+  username: async (s: string) => {
+    const taken = await API.isUsernameTaken(s)
+    return taken ? 'Username is taken': true
+  }
+}
+```
+
 ### Options
 
 Sometimes it's practical to have some different default values when using for example react-native or some other framework where the default `value`, `onChange` and `(e)=> e.target.value` do not apply.