Hello, 

Probably it will be helpful to someone.

First, add click event. Or you can also use mouseUp client event.

For example, like this on the serve in Page_load:

this.WebTextEditor1.Attributes.Add("onclick", "func()");

The same is valid for asp net textbox.

Getting cursor be done like this on the client side:

function getposition() {

var txt1 = $find("<%= webtexteditor1="" clientid="">");

//returns index of first selected character
var start = txt1.getSelection(true);

//returns index of last selected character
var stop = txt1.getSelection(false);
if (stop > start)
    return "SELECTION";
else
     return start;

}

It can be done aslo for usual asp.net textbox like this:

function getposition() {

//code for usual asp net textbox
var txt1 = document.getElementById("TextBox1");
var currentRange = document.selection.createRange();
var selectedText = currentRange.text;
if (selectedText.length != 0)
   return "SELECTION";
var workRange = currentRange.duplicate();
txt1.select();
var allRange = document.selection.createRange();
var len = 0;

while (workRange.compareEndPoints("StartToStart", allRange) > 0) {
   workRange.moveStart("character", -1);
   len++;
}

currentRange.select();

return len;

}

Then, you can either manually implement AJAX, submit or anything you prefer. Also, you can use some Infragistics control for sending data to the server.

For example - webdropdown. Place it in some not visible area of your page. Don't set it's property Visible to false, or you'll not be able to get webdropdown on the client. You can pass then cursor position and any other data as string, like this

function func() {
var position = getposition();
if (position == "SELECTION")
      return;

var wdd= $find("<%= webdropdown1="" clientid="">");
wdd.loadItems(position, true);

}

And then get your position on the server in ItemsRequested event of webdropdwon:

e.Value.

For example:

protected void wdd_ItemsRequested(object sender, DropDownItemsRequestedEventArgs e)
{
    int positionOfCusrsor = Convert.ToInt32(e.Value);

}