How would one add a code highlighting keyword?

If I for example want to highlight Rust code for a code block then I type 3 grave accents and then rust to tell the markdown parser that this is Rust code. Then I write my code and terminate the code block with another 3 grave accents, so that I end up with:

fn main() {
    println!("Ferris here!");
}

But where exactly is this keyword rust defined? I looked at https://github.com/github/linguist but that does not seem to be the right repository. Is there an open source repository where people can contribute new highlighting or keyword aliases and so on? Maybe outside the GitHub organization even?

Hi and welcome - that is the correct repository for the language detection library we use.

The file here:

Includes the up to date list of languages, including any aliases.

This PR is probably a good example of how to propose any changes of your own.