diff --git a/extracted_text_test.py b/extracted_text_test.py
index 60785b7..9eb57b6 100644
--- a/extracted_text_test.py
+++ b/extracted_text_test.py
@@ -52,6 +52,8 @@ def test_align():
     for left, right in seq_align(grapheme_clusters(test1.text), grapheme_clusters(test2.text)):
         left_id = test1.segment_id_for_pos(left_pos) if left is not None else None
         right_id = test2.segment_id_for_pos(right_pos) if right is not None else None
+        # XXX note that deletions and inserts only produce one id + None, UI must
+        #     support this, i.e. display for the one id produced
         el = AlignmentElement(left, right, left_id, right_id)
         alignment.append(el)
         if left is not None: