RE: Form: Add tab to section
Hi
You cannot add a tab inside a section in CRM form.
As suggested by others, you can definitely drop a web resource to have custom tabs anywhere on the form however please note you will end up doing a lot of design and coding to render sub-grids for 1:N and N:N.
I think you can achieve what you want using Tabs and Reference Panel.
community.dynamics.com/.../dynamics-365-reference-panel
www.youtube.com/watch
www.youtube.com/watch
Please note, to take advantage of Dynamics 365 Unified Interface and Performance improvements, you should try and use the out of the box features for form design. When you convert your Dev Express XAF app to CDS, you have to remember you wont be able to replicate the exact layout in CRM. You should rather adopt to CRM UI and try your best to make it look like the XAF app while taking full advantage of UCI by sticking to OOB components as much as you can.
If you definitely have to replicate the XAF UI, I would recommend you look into creating a PCF control rather than going down the webresource path as web resource is not recommended for UCI.
docs.microsoft.com/.../overview