Normally when you navigate to a webpage you want to edit, you get the option to edit the page by clicking the "New Draft" tab.
Sometimes, though, that tab doesn't exist. Instead there are two new options in its place: "View Draft"/"Edit Draft".
This means that someone—yourself, or another web publisher—has created a new draft of the page. Either on purpose, or started making a change and abandoned it. How can you tell the difference?
Yellow highlighting shows that the older page said "to do so" but the newer draft does not have that.