A: 

You can't do that with HTML. Maybe with Javascript. Basically, you just detect double clicks in a certain area and then select the appropriate text.

EDIT:

Here's how to do it in W3C compliant browser (e.g. Firefox, it probably won't work in IE, which isn't a W3C compliant browser and uses different text selection model):

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;

<html>
    <head>
        <script type="text/javascript">
            function select(elem) {
                var sel = window.getSelection();
                var range = sel.getRangeAt(0);
                range.selectNode(elem);
                sel.addRange(range);
            }            
        </script>
    </head>
    <body>
        <p>a simple paragraph, this is 
            <span onclick="select(this);">clickable area</span> 
            when this 
            <span ondblclick="select(this);">span tag is double-clicked</span>
            then they will be selected
        </p> 
    </body>
</html>
Lie Ryan
+1  A: 

Thanks to everyone, but I've managed to do it by using a readonly text field set without borders and with the background color of the background of the website.

Double clicking works as expected, without relying on client-side scripting.

Flavius