I am fairly new to ASP programming and am stuck at what seems like a pretty straight-forward piece of code: the Trim() function.

 <asp:TextBox ID="txtsearch" runat="server" Text="ALL" onblur="if (Trim(this.value) == '') this.value='ALL';"></asp:TextBox>
Why won't this fill the text box with the word 'ALL' if there are only blank spaces in the field? Am I not calling the function correctly?