[css-ruby] Properly escape markup

Author: frivoal

css-ruby-1/Overview.bs

@@ -1594,7 +1594,7 @@ Appendix A: Sample Style Sheets</h2>
 		rt + rtc::before { content: "）（"; }</pre>
 
 	Alternatively, if it is known that a purely alternating style of markup is used
-	(<code>&lt;ruby>A<rt>a</rt>B<rt>b</rt>C<rt>c</rt>&lt;ruby></code>)
+	(<code highlight=html>&lt;ruby>A&lt;rt>a&lt;/rt>B&lt;rt>b&lt;/rt>C&lt;rt>c&lt;/rt>&lt;ruby></code>)
 	where there are no adjacent ruby annotations,
 	the following rules will add parentheses around each annotation: