Making data validation in server

Hi,

How could I validate the entered data in the server-side and warn the user that the data is not valid just-in-time?
I would be something like receiving some sort of return value when sending the HTTP POST request to the server.

Is that possible?
Many thanks,

For what it's worth...I was able to write some code to leverage Microsoft's Atlas webservice capabilities. You could modify this to run any server-side code, and return any result. Currently I do not process any result, I simply use this to save cell-editing values to SQL.

obj.onCellValidated = function(text, column, row)
{
MySaveData(text, column, RowAutoID);
}

function MySaveData(text, column, row)
{
var SrchElem = document.getElementById("SearchKey");
Samples.AspNet.HelloWorldService.UpdateLineItem(row + "|" + column + "|" + text, OnRequestComplete);
}

function OnRequestComplete(result)
{
alert(result);
}

Check also the code in this example -

http://www.activewidgets.com/grid.examples/saving-changed-cells.html

Instead of saving the data you can just do validation with the same code.