Implement a function to get the additional properties on a headline.

src/compare/diff.rs

@@ -542,6 +542,10 @@ fn new_compare_heading<'b, 's>(
     let mut child_status = Vec::new();
     let mut message = None;
 
+    let additional_property_names = rust
+        .get_additional_properties()
+        .map(|node_property| EmacsField::Required(node_property.property_name));
+
     // TODO: This needs to support additional properties from the property drawer
 
     compare_children(