Currently, by having a single implementation, so that there isn't really a "Rust standard" besides what this or that version of the Rust compiler does and what

Currently, by having a single implementation, so that there isn't really a "Rust standard" besides what this or that version of the Rust compiler does and what the documentation says, and if there's a discrepancy, it's a documentation or compiler bug. There might one day be a "Rust standard", but then let's all wish the standardization process leads to something like the Ada Language Reference Manual instead of the mess that is ANSI C.