js的一个小语法问题

Question

<TABLE id="Table2" cellSpacing="0" cellPadding="0" width="111" border="1">
<TR>
<TD colSpan="3"><a href="#" onclick="bbb('pnlVideo','VideoCatalog')"><IMG alt="" src="../image/1-up.gif" name="VideoCatalog"></a></TD>
</TR>
<TR>
<TD colSpan="3">
<asp:Panel id="pnlVideo" runat="server" Height="8px" HorizontalAlign="Center" Width="100%">
<P>
<asp:HyperLink id="HyperLink1" runat="server" CssClass="TextInput">影片发布</asp:HyperLink></P>
<P>
<asp:HyperLink id="HyperLink2" runat="server" CssClass="TextInput">影片删除</asp:HyperLink></P>
</asp:Panel></TD>
</TR>
</TABLE>
<SCRIPT language="javascript">
function bbb(pnl,catalog)
{
var P = pnl;
var C = catalog;
if (document.all(P).style.display == "none")
{
document.all(P).style.display = "";
document.all(C).src = "../image/1-up.gif";
}
else
{
document.all(P).style.display = "none";
document.all(C).src = "../image/1-down.gif";
}
}
</SCRIPT>