title: Make a (collapsible, autosized and always-visible) panel display scrollbar if bigger than the page?
body: <p>I'm working with an asp.net master-page; the relevant code is as follows:</p>
  
  <pre><code>&lt;body&gt;      
    &lt;form id="form1" runat="server"&gt;
      &lt;asp:Panel ID="pnlHeader_TopLeft" runat="server"
       onmouseleave="$find('MenuCollapser').collapsePanel();"&gt;
        &lt;asp:Panel ID="pnlAppTitle"  runat="server"
         onmouseenter="$find('MenuCollapser').expandPanel();"&gt;
           [my title bar]
        &lt;/asp:Panel&gt;
        &lt;asp:Panel ID="pnlMenuMain" Style="float: left; clear: both; 
         runat="server"&gt;
           [my menu items]
        &lt;/asp:Panel&gt;
      &lt;/asp:Panel&gt;
      &lt;ajax:CollapsiblePanelExtender BehaviorID="MenuCollapser"
       TargetControlID="pnlMenuMain" ExpandDirection="Vertical"
       SuppressPostBack="true" Collapsed="true" runat="server" /&gt;
      &lt;ajax:AlwaysVisibleControlExtender TargetControlID="pnlHeader_TopLeft"
       HorizontalSide="left" VerticalSide="Top" runat="server" /&gt;
    &lt;/form&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p>This works perfectly....unless the contents of <code>pnlMenuMain</code> are so numerous that the panel's height expands beyond the page, obscurring its bottom portion.  Is there some way that I can cap its maximum height so that it stops expanding before reaching the screen's max height, and uses a scrollbar instead?</p>