Constant EXEMPT_FEATURES 

const EXEMPT_FEATURES: Features;

These features are left alone by limit bucketing. They will be exposed to higher layers whenever the device supports them, and they are not considered when determining bucket compatibility.

All four features in the list are related to external textures. (The texture format features are used internally by Firefox to support external textures.)

Handling them this way is a bit of a kludge, but is expected to be a short-term situation only until external texture support is universally available.

Note that while NV12 and P010 can be hidden from content by excluding them from WebIDL, TEXTURE_FORMATS_16BIT_NORM will eventually be replaced with TEXTURE_FORMATS_TIER1, and at that point neither excluding the tier1 formats from WebIDL entirely nor allowing content to use them on a device that doesn’t have the feature enabled will be acceptable. See https://github.com/gfx-rs/wgpu/issues/8122.