> It's still kind of a wild west so you see people using the italics d for derivatives instead of the differential operator upright bold form.
Upright and italic are both valid, but I don't think that I've ever seen a bold "d" used for an ordinary (scalar) derivative. I've seen it occasionally used for vector derivatives, but even that's rare.
> I guess because it's hard to type those out compared to "d".
This is intentional in many cases [0]. (But similar things like writing "sin" in italics is never okay and is just pure laziness.)
Upright and italic are both valid, but I don't think that I've ever seen a bold "d" used for an ordinary (scalar) derivative. I've seen it occasionally used for vector derivatives, but even that's rare.
> I guess because it's hard to type those out compared to "d".
This is intentional in many cases [0]. (But similar things like writing "sin" in italics is never okay and is just pure laziness.)
[0]: https://tex.stackexchange.com/questions/14821/whats-the-prop...