docs: Clarify acceptable characters for widget id value (#1108)
diff --git a/www/docs/en/dev/config_ref/index.md b/www/docs/en/dev/config_ref/index.md
index a1cd7a0..31d91be 100644
--- a/www/docs/en/dev/config_ref/index.md
+++ b/www/docs/en/dev/config_ref/index.md
@@ -59,7 +59,7 @@
Attributes(type) <br/> <span class="sub-header">Only for platform:</span> | Description
---------------- | ------------
-id(string) | *Required* <br/> Specifies the app's reverse-domain identifier.
+id(string) | *Required* <br/> Specifies the app's identifier. The `id` should be in a [reverse-DNS format](https://en.wikipedia.org/wiki/Reverse_domain_name_notation#Examples) however, only alphanumeric and dot characters are allowed. e.g: `com.example.myapp`
version(string) | *Required* <br/> Full version number expressed in major/minor/patch notation.
android-versionCode(string) <br/> ==Android== | Alternative version for Android. Sets the [version code](http://developer.android.com/tools/publishing/versioning.html) for the application. See [the Android guide](../guide/platforms/android/index.html#setting-the-version-code) for information on how this attribute may be modified.
ios-CFBundleVersion(string) <br/> ==iOS== | Alternative version for iOS. For further details, see [iOS versioning](https://developer.apple.com/library/ios/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html#//apple_ref/doc/uid/20001431-102364).
