OptionalalphaAlpha in the drawing buffer, so a canvas can composite with the page.
OptionalantialiasMultisampling; driven by RendererOptions.antialias (§45).
OptionaldepthA depth buffer — required, since every view clears and tests depth (§61).
OptionalstencilStencil bits for §67's masks and clips, driven by
RendererOptions.stencil (R-7; consumed by R-23's node-level clips).
false unless asked — the attribute every renderer built before R-7 got.
Context attributes this backend requests (a subset of WebGL's
WebGLContextAttributes).Only the four that the MVP has an opinion about are named; everything else is left at the browser's default, because requesting a value the engine does not use is how a backend ends up with a framebuffer nobody asked for.