多行文本框超长验证

 <span class="e_text_tip">(0~500字)&nbsp;</span><asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="TXTpcdescripton"
                Display="Dynamic" ErrorMessage="超长" ValidationExpression="^(.|\n){0,500}$" CssClass="e_text_errortip"></asp:RegularExpressionValidator>