Function value_differences 

pub fn value_differences(
    original: &GffStruct,
    rewritten: &GffStruct,
) -> Vec<ValueDifference>

Reports every field the rewrite changed the value of.

Walks the rewritten tree and compares each field against the original’s field of the same label, recursing into nested structs. A label the original does not carry is skipped here; that case is what LabelCensus exists for.

Lists are skipped entirely. Element order in a rewrite is the view’s, not the file’s, so a positional comparison reports differences that are not defects. A caller that models a list’s contents compares them directly.