Add breaklines = true to the example document's \lstset

example/mu/example.dtx

@@ -413,13 +413,15 @@
 \usepackage{markdown} %% Lightweight markup
 \usepackage{listings} %% Source code highlighting
 \lstset{
-  basicstyle      = \ttfamily,%
-  identifierstyle = \color{black},%
-  keywordstyle    = \color{blue},%
-  keywordstyle    = {[2]\color{cyan}},%
-  keywordstyle    = {[3]\color{olive}},%
-  stringstyle     = \color{teal},%
-  commentstyle    = \itshape\color{magenta}}
+  basicstyle      = \ttfamily,
+  identifierstyle = \color{black},
+  keywordstyle    = \color{blue},
+  keywordstyle    = {[2]\color{cyan}},
+  keywordstyle    = {[3]\color{olive}},
+  stringstyle     = \color{teal},
+  commentstyle    = \itshape\color{magenta},
+  breaklines      = true,
+}
 \usepackage{floatrow} %% Putting captions above tables
 \floatsetup[table]{capposition=top}
 %<*econ>