If you comment on a friend's status update, link or photo, you can now press the 'X' in the top right corner to edit it. Your comment instantly turns into a text box where you can alter what you've written; then just press Enter to save it again.
There are some caveats, though! First, if someone comments after you, your comment is locked; you can still delete it, but you can't edit. Second, there seems to be some kind of time limit on editing. The editing window might be as short as 60 seconds. Still, for those of you that have 'accidentally' submitted comments by pressing Enter, the ability to edit is a godsend.
It's also worth noting that everyone still gets email (and SMS!) notifications when you comment, and when you edit comments.
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