Function traversal 

pub fn traversal<'a, F, V>(
    sd: &'a StructureDefinition,
    visitor: &mut F,
) -> Result<V, String>
where
    F: FnMut(&'a ElementDefinition, Vec<V>, usize) -> V,

Traverses the elements of a [StructureDefinition] in bottom-up order.

The visitor function is called after all child elements have been traversed.

Errors

Returns an error if the [StructureDefinition] does not contain a snapshot.