Use a textarea for custom navigation.

src/General/Header.coffee

@@ -122,7 +122,7 @@ Header =
     $.add Header.bar, [boardList, Header.shortcuts, Header.notify, Header.toggle]
 
     Header.setCustomNav Conf['Custom Board Navigation']
-    Header.generateBoardList Conf['boardnav']
+    Header.generateBoardList Conf['boardnav'].replace /(\r\n|\n|\r)/g, ' '
 
     $.sync 'Custom Board Navigation', Header.setCustomNav
     $.sync 'boardnav', Header.generateBoardList

src/General/html/Settings/Advanced.html

@@ -5,7 +5,7 @@
 </fieldset>
 <fieldset>
   <legend>Custom Board Navigation</span></legend>
-  <div><input name=boardnav class=field spellcheck=false></div>
+  <div><textarea name=boardnav class=field spellcheck=false></textarea></div>
   <div>In the following, <code>board</code> can translate to a board ID (<code>a</code>, <code>b</code>, etc...), the current board (<code>current</code>), or the Status/Twitter link (<code>status</code>, <code>@</code>).</div>
   <div>
     For example:<br>
@@ -24,6 +24,7 @@
   <div>External link: <code>external-text:"Google","http://www.google.com"</code></div>
   <div>Combinations are possible: <code>board-index-text:"VIP Index"</code></div>
   <div>Full board list toggle: <code>toggle-all</code></div>
+  <div>Line breaks are allowed and will be replaced with spaces</div>
 </fieldset>
 
 <fieldset>