HTML tooltip using only div/span/etc. attributes (onmouse…/style/etc.)

I work with a website that has a rich text box which gives direct access to the underlying HTML code. I can edit the HTML code, but when I save it, the website intervenes. <style> elements disappear, but <div> and <span> elements remain and seem to keep all their attributes.

I would like a certain <span> element to show a tooltip when hovered over. I’ve considered using the title attribute (it works), but it’s not flexible enough for my need.

Is it possible (and how) to implement a tooltip like shown here without a <style> element, using only attributes of <div> and <span> elements? I was thinking of attributes such as style, onmouseover, and onmouseout, but feel free to suggest other ones as you see fit.