I was just looking at this library in comparison to other libraries that do sourcemap manipulation, and found it confusing to get started because of the extra requirement that the library is initialized with web assembly. It seems like much of the explanation of the workings was done in a blog post: https://hacks.mozilla.org/2018/01/oxidizing-source-maps-with-rust-and-webassembly/

Specifically, I think the documentation is incomplete because:

• It does not explain where the source of mappings.wasm is defined- it appears to be a separate package, but there is also a version checked into the repo.
• While there is mention of initializing via ArrayBuffer Add option to initialize mappings wasm via ArrayBuffer #339, there is no example.
• The blog post I read defines mapping_callback as the key interface for the .wasm code- this seems like an important part to include in a README