Some functions have extra, undocumented arguments in libsodium.js

[Jack-Edwards]

To help reduce the amount of allocations and copying of data when calling libsodium.js from a C# language binding (Blazor), I'm hoping to use some of the "lower level" libsodium functions in libsodium.js. However, I'm finding that many of the functions contain extra, undocumented arguments.

For example:
crypto_box_easy

The "target" function takes 7 arguments. The official documentation only describes 6 arguments. What is the extra argument?

Another example would be crypto_secretstream_xchacha20poly1305_push, which takes 10 arguments instead of 8.

More information: Jack-Edwards/BlazorSodium#34