I tried to create a custom exception class (per the documentation here:
When I tried, Welkin told me that it was unable (see attached screenshot). I tried creating other classes, with various names. Without exception (haha funny joke), it would fail if the name ended with "Exception" and it would succeed if the name did NOT end with "Exception". I was able to create the desired class just fine via the Salesforce GUI in my browser.
I am using TWS 0.29.10.4