Starting with v15.2, the new XAF web UI provides a built-in solution for this task. Please see a screenshot from our XCRM demo:



You can enable this feature for required layout groups in the Model Editor via the new IsCollapsibleCardGroup option at the Views | <DetailView> | Layout | level:



Note that at the moment collapsed groups state is not currently stored/restored between sessions.  If you want to learn more on accomplishing this task in WinForms apps or wish to implement a fully custom-tailored ASP.NET solution, check out the How do I provide the capability to collapse or expand layout groups and persist their state? thread in the Support Center for additional information.

As always, I look forward to hearing from you on this small feature in comments!