Compare value.

src/compare/diff.rs

@@ -1208,9 +1208,20 @@ fn compare_comment<'b, 's>(
     rust: &'b Comment<'s>,
 ) -> Result<DiffEntry<'b, 's>, Box<dyn std::error::Error>> {
     let child_status = Vec::new();
-    let this_status = DiffStatus::Good;
-    let message = None;
-    // TODO: Compare :value
+    let mut this_status = DiffStatus::Good;
+    let mut message = None;
+
+    // Compare value
+    let value =
+        get_property_quoted_string(emacs, ":value")?.ok_or("Comments should have a value.")?;
+    let rust_value = rust.get_value();
+    if value != rust_value {
+        this_status = DiffStatus::Bad;
+        message = Some(format!(
+            "Value mismatch (emacs != rust) {:?} != {:?}",
+            value, rust_value
+        ));
+    }
 
     Ok(DiffResult {
         status: this_status,