Function parse_field 

pub fn parse_field<T: Packed + Debug>(
    width: u32,
    given: &str,
) -> Result<T, FieldError>

Parse a field’s value out of the way the field prints it.

The rendering is the vocabulary: this walks the field’s own bit patterns and takes the one whose Debug matches, so a type gets string parsing from its Debug alone, and a value outside its range has no pattern to match and fails here rather than being clamped.

⚠️ An unexplained value can therefore only be written by naming it as unexplained: a sparse enum renders an unrecognized 9 as Unknown(9), so a bare 9 matches nothing and Unknown(9) is the only spelling.