LeftAndMain seems to be changed comparing to 2.4 (_left and _right templates are replaced with other suffixes, etc.) and there's no doc page for it for 3.0 that I could find. I'd also be interested in advanced usage of custom forms in the admin panel -- by "advanced" I mean stuff like extending LeftAndMain an using a Form instead of just using ModelAdmin that isn't very customizable.
I would love to understand how it all goes from request to form to POST to DB saving to confirmation to reloading AJAX parts of the GUI. It's all just trial and error and analyzing CMSMain and similar code which isn't the simplest thing to do since PHP has so much "magic" stuff that seems to be used. Ctrl-click in my IDE seems unhelpful anyway.
Does anyone use SilverStripe as something more than a CMS with a kick, or is it unusual for me to try to add more advanced forms in the admin panel and to take control of it? Are there any docs for people like me?