Milestones
A milestone groups issues toward a target. Manage them at
/:owner/:repo/milestones.
Creating a milestone
A title, an optional description, and an optional due date.
Progress
Progress is the ratio of closed issues to total issues in the milestone. It is a measured ratio, not an estimate, so it moves only when an issue actually closes.
Closing a milestone
Closing does not close the issues inside it. Open issues in a closed milestone stay open and stay visible — hiding them would make the milestone look finished when it is not.