diff --git a/API.md b/API.md
index c534b64f..71992443 100644
--- a/API.md
+++ b/API.md
@@ -659,6 +659,8 @@ Formsy.addValidationRule('isMoreThan', function (values, value, otherField) {
 ```
 Returns true if the value is thruthful
 
+_For more complicated regular expressions (emoji, international characters) you can use [xregexp](https://github.com/slevithan/xregexp). See [this comment](https://github.com/christianalfoni/formsy-react/issues/407#issuecomment-266306783) for an example._
+
 **isEmail**
 ```jsx
 <MyInputComponent name="foo" validations="isEmail"/>