CSS3D and WebGL

Both CSS and WebGL have their strong points, in different scenarios.
For example, HTML/CSS3D input-elements are very optimized for smartphone-users.
Iframe-elements however, are Here's a small performance-matrix which SearXR uses to decide which ui-technology has the best performance/UX-ratio:

scenarioHTML/CSS3D
ui-elements
HTML-2-canvas
ui-elements
(AFRAME)
WebGL
custom
ui elements
Iframe (*)
smartphone AR
tablet AR
desktop 3D
smartphone VR
headset VR

* = only same-origin iframe's can ensure a nice UX.

NOTE: the pattern seems to be, that stereoscopic vision automatically disqualifies HTML/CSS3D.

Rule engine to the rescue

SearXR uses a tiny rule engine for feature-sensemaking.
Basically, functions only fire when certain conditions are met:

ps. click image for enlarged version