diff --git a/options.xhtml b/options.xhtml
index 2ac4e3dd1..95be49708 100644
--- a/options.xhtml
+++ b/options.xhtml
@@ -38058,7 +38058,7 @@ keyboard.</p></dd><dt><span class="term"><code class="literal">register</code></
 commands like <code class="literal">:set-mark</code>.</p></dd></dl></div>
 
 <p><span class="emphasis"><em>Type:</em></span>
-attribute set of attribute set of strings concatenated with &quot; ;; &quot;</p>
+attribute set of attribute set of (null or strings concatenated with &quot; ;; &quot;)</p>
 
 <p><span class="emphasis"><em>Default:</em></span>
 <code class="literal">{ }</code></p>