Selector in tooltip widget

Selector in tooltip widget

Hi,

I'm with an issue for a long time and I don't manage to find any solution on the internet. So here is my question :

I have a table in which each cell has a different class. But I would like to show a tooltip only on cells which have a specific class. So in 'selector' of the tooltip, I put the corresponding class but nothing happens ! Whereas when I put 'document', it shows a tooltip but for all cells...
Here is my code :
  1. $('.creature').tooltip({
            show: {effect: "slideDown", delay: 100},
            position: {my: "bottom", at: "top"}
            });

In this case, I would like that all the cells of my table with class "creature" shows a tooltip but it doesn't work...

And more, how is it possible to select various class for just one tooltip function ?

Someone could help me ?