* About the name itself: i've considered `is_rtr()` but discarded it to remain coherent with other method names in this trait (like: `is_extended()`, and not: `is_eff()`).
The philosophy seems to be: short yet descriptive names, that do not require intimate knowledge of every flag of the underlying protocol (fwiw, i believe this is indeed the right level of abstraction for this trait).

There's just one outlier: `dlc()`. I guess `data_length_code()` is a mouthful breaking the "short" constraint…
And `data_length()` could be misleading in the case of a `request_frame`, as it has no data, even when yet its `dlc` is non-zero.