Element visibilty and DOM changes listener

We use a search field with an autosuggest dropdown. I already track suggestions that are being clicked on and I could also track when the input field is going into focus.

But what I really like to know is how many people actually start typing and have suggestions presented to them.

In GA I would use element visibility and watch for DOM changes. For instance: the class of the element changes from closed to open.

I do not see this option in MTM, am I missing something or is there another way of doing this?