How to know if selected text is inside a specific div

I have two divs as shown below:

<div id="div1">
<p>something</p>
<div><table><tr><td>Div1</td></tr></table></div>
</div>
<div id="div2">
<p>something else</p>
<div><table><tr><td>Div2</td></tr></table></div>
</div>
<button type="button">Check</button>

Now, I want to know when some text is selected and then the button pressed, if the selected text is under "div1" or not. How can I do that?

Edit: And the solution has to work in IE-7 and above.

Solution 1:

The elementContainsSelection() function below returns a boolean representing whether the specified element contains the whole of the user's selection and works in all major browsers, including IE 6.

Live demo: http://jsfiddle.net/eT8NQ/

Code:

function isOrContains(node, container) {
    while (node) {
        if (node === container) {
            return true;
        }
        node = node.parentNode;
    }
    return false;
}

function elementContainsSelection(el) {
    var sel;
    if (window.getSelection) {
        sel = window.getSelection();
        if (sel.rangeCount > 0) {
            for (var i = 0; i < sel.rangeCount; ++i) {
                if (!isOrContains(sel.getRangeAt(i).commonAncestorContainer, el)) {
                    return false;
                }
            }
            return true;
        }
    } else if ( (sel = document.selection) && sel.type != "Control") {
        return isOrContains(sel.createRange().parentElement(), el);
    }
    return false;
}