How to insert an element at selected position in HTML document?

I want to insert an element(span,div etc) at the position determined by user selection of text in the document.

I was able to get the element on which selection is made. But I am not able to get the exact position where the selection is made.

For example:

<span>this is testing string for testing purpose</span>

In this, lets assume 开发者_JS百科that user selected 2nd 'testing' word. I want it to be replaced like

<span>this is testing string for <b>testing</b> purpose</span>

How do i do it?

BTW: I know it is possible. Google Wave does it. I just dont know how to do it

This will do the job:

function replaceSelectionWithNode(node) {
    var range, html;
    if (window.getSelection && window.getSelection().getRangeAt) {
        range = window.getSelection().getRangeAt(0);
        range.deleteContents();
        range.insertNode(node);
    } else if (document.selection && document.selection.createRange) {
        range = document.selection.createRange();
        html = (node.nodeType == 3) ? node.data : node.outerHTML;
        range.pasteHTML(html);
    }
}

var el = document.createElement("b");
el.appendChild(document.createTextNode("testing"));
replaceSelectionWithNode(el);

The method for retrieving the current selected text differs from one browser to another. A number of jQuery plug-ins offer cross-platform solutions.

(also see http://api.jquery.com/select/)

See here for working jsFiddle: http://jsfiddle.net/dKaJ3/2/

function getSelectionHtml() {
    var html = "";
    if (typeof window.getSelection != "undefined") {
        var sel = window.getSelection();
        if (sel.rangeCount) {
            var container = document.createElement("div");
            for (var i = 0, len = sel.rangeCount; i < len; ++i) {
                container.appendChild(sel.getRangeAt(i).cloneContents());
            }
            html = container.innerHTML;
        }
    } else if (typeof document.selection != "undefined") {
        if (document.selection.type == "Text") {
            html = document.selection.createRange().htmlText;
        }
    }
    alert(html);
}