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(

src/types/document.rs

@@ -2,6 +2,7 @@ use std::path::PathBuf;
 
 use super::Element;
 use super::GetStandardProperties;
+use super::NodeProperty;
 use super::Object;
 use super::StandardProperties;
 use super::Timestamp;
@@ -90,4 +91,23 @@ impl<'s> Heading<'s> {
             .collect();
         title_source
     }
+
+    pub fn get_additional_properties(&self) -> impl Iterator<Item = &NodeProperty<'s>> {
+        let foo = self
+            .children
+            .iter()
+            .take(1)
+            .filter_map(|c| match c {
+                DocumentElement::Section(section) => Some(section),
+                _ => None,
+            })
+            .flat_map(|section| section.children.iter())
+            .take(1)
+            .filter_map(|element| match element {
+                Element::PropertyDrawer(property_drawer) => Some(property_drawer),
+                _ => None,
+            })
+            .flat_map(|property_drawer| property_drawer.children.iter());
+        foo
+    }
 }