ajaxToolkit:TextBoxWatermarkExtender演示与实现代码

<asp:TextBox ID="txtCCEmail" runat="server" TextMode="MultiLine" Height="50" CssClass="textbox" 
Width="250"></asp:TextBox><br /> 
<ajaxToolkit:TextBoxWatermarkExtender ID="TextBoxWatermarkExtender3" runat="server" 
TargetControlID="txtCCEmail" WatermarkText="sample1@yourcompany.com; sample2@yourcompany.com;" 
WatermarkCssClass="watermarked"> 
</ajaxToolkit:TextBoxWatermarkExtender>