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:
* = 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: