Supplementary for the retainPortal option

mkdocs/apiconfig.md

@@ -226,6 +226,9 @@ Specify whether to continue the portal function even if the captive portal timed
 !!! hint "Connection request after timed-out"
     With the **retainPortal**, even if AutoConnect::begin in the setup() is timed out, you can execute the sketch and the portal function as a WiFi connection attempt by calling AutoConnect::handleClient in the loop().
 
+!!! info "All unresolved addresses redirects to /_ac"
+    If you enable the **retainPortal** option, **all unresolved URIs will be redirected to `SoftAPIP/_ac`**. It happens frequently as client devices repeat captive portal probes in particular. To avoid this, you need to exit from the WiFi connection Apps on your device once.
+
 ### <i class="fa fa-caret-right"></i> staip
 
 Set a static IP address. The IP will behave with STA mode.

mkdocs/lsbegin.md

@@ -11,10 +11,12 @@ You can use these parameters in combination with sketch requirements and need to
 
 <img align="center" src="images/process_begin.svg">
 
-For example, AutoConnect::begin will not exits without the **portalTimeout** while the connection not establishes, but WebServer will start to work. So, your sketch may work seemingly, but it will close with inside a loop of the AutoConnect::begin function. Especially when invoking AutoConnect::begin in the **setup()**, execution control does not pass to the **loop()**.
+For example, AutoConnect::begin will not exits without the **portalTimeout** while the connection not establishes, but WebServer will start to work. A DNS server that detects the probe of the captive portal is also effective. So, your sketch may work seemingly, but it will close with inside a loop of the AutoConnect::begin function. Especially when invoking AutoConnect::begin in the **setup()**, execution control does not pass to the **loop()**.
 
 As different scenes, you may use the **immediateStart** effectively. Equipped the external switch to activate the captive portal with the ESP module, combined with the **portalTime** and the **retainPortal** it will become WiFi active connection feature. You can start AutoConnect::begin at any point in the **loop()**, which allows your sketch can behave both the offline mode and the online mode.
 
+The **retainPortal** option allows the DNS server to continue operation after exiting from AutoConnect::begin. AutoConnect traps captive portal detection from the client and redirects it to the AutoConnect menu. That trap will answer all unresolved addresses with SoftAP's IP address. If the URI handler for the source request is undefined, it returns a 302 response with `SoftAPIP/_ac` to the client. This is the mechanism of AutoConnect's captive portal. Captive portal probes will frequently occur while you are attempting on the client device's WiFi connection Apps and these implementations are varied each OS, so it not realistic to identify all probing URIs. Therefore, while retainPortal is enabled, it is not preferable to executing the sketch under the WiFi connection Apps on the client device. (Probably not work correctly) You need to exit from the WiFi connection Apps once.
+
 Please consider these kinds of influence when you make sketches.
 
 !!! info "The AutoConnect::begin 3rd parameter"