diff --git a/example/mu/example.dtx b/example/mu/example.dtx
index 51def6381d484f8b719ecff3a8962ec2f430d865..2c9d4436fb63807298424f8b5c44e97d24d81041 100644
--- a/example/mu/example.dtx
+++ b/example/mu/example.dtx
@@ -149,6 +149,15 @@
 
       span multiple paragraphs.
     },
+    %% The following key is only useful when you are writing a
+    %% doctoral thesis. You can safely omit it in other theses.
+    extra              = {
+      summary          = {%
+        This is the summary of my thesis, which should
+
+	not be very long.
+      },
+    },
 }
 %</econ>
 %<*fi>
@@ -374,6 +383,15 @@
       span multiple paragraphs.
     },
     bib        = example.bib,
+    %% The following key is only useful when you are writing a
+    %% doctoral thesis. You can safely omit it in other theses.
+    extra      = {
+      summary  = {%
+        This is the summary of my thesis, which should
+
+        not be very long.
+      },
+    },
 }
 %</phil>
 %<*sci>