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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
I'm not sure which "flexible blocking" methods you were implying to, as I see it's still just "blocking" and "allowing" for most of the "extensions" on safari, and do they publish source code and documentations for those methods; comparing to redirection, denyallow... (in ublock and adguard) or script defusing methods I said above?
The limitation makes the users unable to neutralize malicious/tracking scripts and other resources from websites. You can search for safari in many adguard filter lists in which they have to allow (@@) many resources to be loaded as the websites use them for anti-adblock and breaking things on their own sites, unlike gecko and (current) chromium (future chromium will have this limitation too, as they also drops webRequest.