I created this demo in response to a post in the Clarion newsgroups asking about how to shorten the window titles when using the MDI tab feature of Clarion on an appframe.
Here is a demo app in C11 that shows how to do it.
https://www.clarionproseries.com/download/SubClassMDITabs.zip
It has five MDI windows and the code applied to three of them so you can
see how it works and what it is like without it.
I hope this helps someone in the future!
Charles