Depending on what your language is for you probably want both.
WUFFS type base.u8[0 ..= 42] is a type which fits in one byte but only has values zero through 42 inclusive, and it's a different type from base.u32[0 ..= 42] because that one takes four bytes.
Rust cares about this stuff to some extent but only internally, for types with a "niche" where it can squirrel away the None case of Option in an invalid value without needing more space. e.g. Rust's optional pointer is the same size as a traditional C-style pointer, because NULL isn't a valid pointer value so that means None, and Rust's optional NonZeroU64 is the same size as a u64 (64-bits) because zero isn't valid so that means None.
WUFFS type base.u8[0 ..= 42] is a type which fits in one byte but only has values zero through 42 inclusive, and it's a different type from base.u32[0 ..= 42] because that one takes four bytes.
Rust cares about this stuff to some extent but only internally, for types with a "niche" where it can squirrel away the None case of Option in an invalid value without needing more space. e.g. Rust's optional pointer is the same size as a traditional C-style pointer, because NULL isn't a valid pointer value so that means None, and Rust's optional NonZeroU64 is the same size as a u64 (64-bits) because zero isn't valid so that means None.