Macro features_web 

macro_rules! features_web {
    (FeaturesWebGPU; $($flag:tt [$($web:tt)?])*) => { ... };
    ($inner_name:tt; $($flag:tt [$($web:tt)?])*) => { ... };
}

Generate the Features::ALLOWED_ON_WEB_BACKEND constant.

Each FeaturesWebGPU feature must have the web attribute, specifying whether or not to expose it on the web backend (typically yes, unless there are known deficiencies in the bindings that prevent using the feature). Standards-track native-only features can be added as special cases.