facility to "edit" a comment or a post

there should be facility to "edit" own comments(available atleast for some minutes after posting). right now you can only "delete" own comment, but not "edit".

"editing" is needed because sometimes we need to reformat our own comment or correct the grammatical mistakes.

atleast, If providing "editing" facility is too much effort, then atleast facility to optionally "Preview" the comment ,before-posting is needed