You can edit your microposts to correct a typo, fix a link or whatsoever.
After saving an edited micropost, it will be marked as "edited", so that others are aware that the post has been modified.
Click the "(edited)" link to show a version history overlay. It includes all modifications that have been made to this post, including date, time, the modifying user and the post contents.
Editing a micropost will not change the order of the timeline. The edited micropost will not be on top.