Historical note, it was originally done as UE3 to Flash C++ Crossbridge / Stage 3D, the WebGL version came later.

https://www.shacknews.com/article/72813/epic-releases-epic-c...

"Unreal Engine 3 Support for Adobe Flash Player - Epic Citadel"

-- https://www.youtube.com/watch?v=xzyCTt5KLKU

https://adobe-flash.github.io/crossbridge/

https://help.adobe.com/en_US/as3/dev/WSF24A5A75-38D6-4a44-BD...