How to change Tooltip for date type in dynamic form

[vikramvsc]

By default, Smartclient 6.5.x version display "Show Date chooser" as tool tip on mouse over event on calender icon display besides dateitem of dynamic form.
We need to change this "Show Date chooser" to some custom message. I tried with "prompt" attribute but it didn't resolve it. Please tell me how I can change this tool tip to some custom tool tip like "Show Date".

this.manageForm = isc.DynamicForm.create({ID:"manageForm",colWidths:"30%,30%,15%,25%",autoDraw:false, wrapItemTitles:false,numCols:4,rowSpan:7,width:"100%",height:"100%",autoFocus:true,
fields:[{name:"countryCode",height:gsmaFormItemHeightVal, type:"select",title:"Country*",titleOrientation:"left", required:true}, 
	{name:"startTN",height:gsmaFormItemHeightVal, type:"text", title:"Start TN*", titleOrientation:"left", defaultValue:"",length:14,required:true},
	{name:"expiryDate",height:gsmaFormItemHeightVal,type:"date",title:"Expiry date ", useTextField:false,inputFormat:"MDY"}
	]
});

Thanks in Advance.