Undo previous action

I really need some kind of “undo” feature. For instance, I recently starred an item without noticing that I had somehow “checked” every item in my library. I have no idea why these were all checked, but the result was that I starred all my items. The only option was to un-star all the items, which had the effect of clearing the 13 stars I had previously assigned. This is a serious problem which could have been avoided if there was some way to star items. (A warning when an action will affect > 100 entries might also be nice.)