The bitflags! macro lets you define all of your flags and their underlying type (in our case, this is u32)[4 to 15]. They are written in ALL_CAPS because they are constants. We can also define collections of flags this way, as we did with ALL[10]. We could have added additional combinations, for example:

const SPICY = Self::PEPPER.bits | Self::CHILI.bits;

The macro then creates a struct with the specified members for you and implements a bunch of traits for it in order to enable the familiar |, &, -, and ! notations [37 to 40] and pretty printing. You can still access the raw bits used in the background directly over the member of the same name.

Note that, when printing, flag combinations will be listed separately. For instance, look at the output in line [47]. After setting all possible flags in the field to active, it will pretty print itself as the following:

Custom spice after adding saffron: SALT | PEPPER | CHILI | SAFFRON | ALL

A useful method to additionally...