Get and Set WaterMark Text of AJAX

Hii  ,I will tell You how can we get Watermark text of Ajax Tool through Javascript
This Can be done by setting Behaviour Id of Watermark Extneder


<asp:TextBox runat="server" ID="txtproId" CssClass="invisible"  />
                                                <cc1:TextBoxWatermarkExtender ID="wtmProjectName" runat="server" BehaviorID="projCatbehav" TargetControlID="txtProjectCategory"
                                                    WatermarkCssClass="watermarked" WatermarkText="Goldy" />

function validate() {

}

To get the Text 

var procat11= $find("projCatbehav").get_Text();

Note:-projCatbehav is an Behaviour Id

To Set the Text

$find("projCatbehav").set_Text("Please Type Here");