How to use TextBoxWatermarkExtender in asp.net ajax

TextBoxWatermarkExtender
TextBoxWatermarkExtender is an asp.net ajax control toolkit's extender control. TextBoxWatermarkExtender control can be attached to an asp.net TextBox web server control. TextBoxWatermarkExtender control apply watermark behavior on target TextBox server control.

When a watermarked textbox control is empty, it display a message in the text input area of the textbox with a custom css style. if someone typed some text into the textbox control, the watermarked appearance goes away.

TextBoxWatermarkExtender control's properties are TargetControlID, WatermarkText and WatermarkCssClass.

TargetControlID property specify the TextBox server control which we want to extend for attach watermark behavior. WatermarkText property set the message which we want to display in TextBox control when textbox has no value. WatermarkCssClass represent a css class which we want to apply into the textbox control when textbox has no value.

Typically asp.net developers use a watermarked TextBox to display additional instruction to input text in TextBox without wasting any space in web page.

The following asp.net ajax example source code demonstrates us how can we use TextBoxWatermarkExender control in web pages.
UsingTextBoxWatermarkExtender.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

<!DOCTYPE html>

<script runat="server">
    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = "Subscription Successful!";
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Ajax TextBoxWatermarkExtender - How to use TextBoxWatermarkExtender in asp.net ajax</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:DarkBlue; font-style:italic;">Ajax Control Toolkit Example: Using TextBoxWatermarkExtender</h2>
        <hr width="550" align="left" color="LightBlue" />
        <asp:ScriptManager 
            ID="ScriptManager1"
            runat="server"
            >
        </asp:ScriptManager>
        <cc1:TextBoxWatermarkExtender 
            ID="TexBoxWatermarkExtender1"
            runat="server"
            TargetControlID="TextBox1"
            WatermarkText="Input your email"
            >
        </cc1:TextBoxWatermarkExtender>
        <br />
        <asp:Label 
            ID="Label1"
            runat="server"
            ForeColor="OrangeRed"
            Font-Bold="true"
            Font-Size="Large"
            >
        </asp:Label>
        <br /><br />
        <asp:TextBox 
            ID="TextBox1"
            runat="server"
            ForeColor="SeaGreen"
            >
        </asp:TextBox>
        <asp:Button 
            ID="Button1"
            runat="server"
            Text="Subscribe RSS Feed"
            OnClick="Button1_Click"
            Height="30"
            Font-Bold="true"
            ForeColor="Green"
            />
    </div>
    </form>
</body>
</html>
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