| A crate is a compilation unit in Rust. Whenever `rustc some_file.rs` is called, |
| `some_file.rs` is treated as the *crate file*. If `some_file.rs` has `mod` |
| declarations in it, then the contents of the module files will get merged with |
| the crate file *before* running the compiler over it. In other words, modules |
| do *not* get compiled individually, only crates get compiled. |
| |
| A crate can be compiled into a binary or into a library. By default, `rustc` |
| will produce a binary from a crate. This behavior can be overridden by passing |
| the `--crate-type` flag to `rustc`. |
