Add documentation for the UseOldExceptionBehavior runtime setting

Author: atennapel-mx

content/en/docs/refguide/runtime/custom-settings/_index.md

@@ -85,6 +85,7 @@ The following custom settings can be configured:
 | <a id="UploadedFilesPath" href="#UploadedFilesPath">UploadedFilesPath</a> | The location of the uploaded files. A valid path can be: `\\FileServer\CustomerPortalFiles`. | [deployment folder]\data\files |
 | <a id="EnableFileDocumentCaching" href="#EnableFileDocumentCaching">EnableFileDocumentCaching</a> | Defines whether file documents should be cached. Only enable this if you are sure that the file documents will not contain sensitive information. Images are always cached. | false |
 | <a id="mapping.import.MaxJsonReadingLength" href="#mapping.import.MaxJsonReadingLength">mapping.import.MaxJsonReadingLength</a> | The maximum length of the JSON string received from the remote which can be processed with import mapping. Use this setting when you expect a string which is longer than the default. See [Import Mappings](/refguide/import-mappings/#troubleshooting) for more information. | 20000000 *(dependent on library version)* |
+| <a id="UseOldExceptionBehavior" href="#UseOldExceptionBehavior">UseOldExceptionBehavior</a> | Allows to set the exception message and wrapping behavior in the Mendix Runtime Server to the behavior before 11.6.0. From 11.6.0 we changed the way messages are constructed preventing that the actual cause of the error might get hidden in the details and exception wrapping is reduced significantly.<br/><br/>The consequence of this change is that error messages will be different with the introduction of this change. And due to the reduction of exception wrapping there is a significant less deep exception nesting, meaning that code depending on finding some specific exception hardcoded on X levels deep (using `exception.getCause().getCause()` for example), will likely start to fail.<br/><br/>To restore the previous behavior and error message set `UseOldExceptionBehavior` to `true`. | false *Introduced in Mendix 11.6.0.* |
 
 ### ApplicationRootUrl {#applicationrooturl-section}