Vendor things

third-party/vendor/web-sys/README.md

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+# `web-sys`
+
+Raw bindings to Web APIs for projects using `wasm-bindgen`.
+
+* [The `web-sys` section of the `wasm-bindgen`
+  guide](https://rustwasm.github.io/wasm-bindgen/web-sys/index.html)
+* [API Documentation](https://rustwasm.github.io/wasm-bindgen/api/web_sys/)
+
+## Crate features
+
+This crate by default contains very little when compiled as almost all of its
+exposed APIs are gated by Cargo features. The exhaustive list of features can be
+found in `crates/web-sys/Cargo.toml`, but the rule of thumb for `web-sys` is
+that each type has its own cargo feature (named after the type). Using an API
+requires enabling the features for all types used in the API, and APIs should
+mention in the documentation what features they require.
+
+## How to add an interface
+
+If you don't see a particular web API in `web-sys`, here is how to add it.
+
+1. Copy the WebIDL specification of the API and place it in a new file in the
+   `webidls/unstable` folder. You can often find the IDL by going to the MDN
+   docs page for the API, scrolling to the bottom, clicking the
+   "Specifications" link, and scrolling to the bottom of the specification
+   page. For example, the bottom of the [MDN
+   docs](https://developer.mozilla.org/en-US/docs/Web/API/MediaSession) on the
+   MediaSession API takes you to the
+   [spec](https://w3c.github.io/mediasession/#the-mediasession-interface). The
+   [very bottom](https://w3c.github.io/mediasession/#idl-index) of _that_ page
+   is the IDL.
+2. Annotate the functions that can throw with `[Throws]`
+3. Run `cargo run --release --package wasm-bindgen-webidl -- webidls src/features ./Cargo.toml`
+4. Run `git add .` to add all the generated files into git.