Allow users to undo changes to layers, such as symbology or label changes usin ghe undo/redo buttons. Right now these tools only seems to work for undoing removal of layers from the table of contents, or actual edits to data. I think you can undo updates to page layout elements too, but only certain things like moving elements around or removing them. I think currently if you change all the internal properties of a rather complex legend element, you can't undo the changes