“Date pickers” are a part of web interfaces that are often overlooked by designers, and for good reason. They are common, complicated, and importantly, they already work. I was in charge of re-designing the datepicker and appointment scheduler for Asurion’s Global Design System, and it was a humbling reminder that reinventing the wheel is often not a great idea.
As I’ve mentioned elsewhere, accessibility is critical in design of all kinds. You as the designer often have a limited idea of what limitations or restrictions your users might be operating under — whether physical, psychological, or technical. In the case of building design systems, your users are other designers and developers, and the same rules apply.
Writing documentation that is as close to universally-understandable as possible is key to the long-term success of any branded design language.