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Didn't it cross your mind to click the "help" link to the right, below the "Add Comment" button? The answer is the very first sentence in this help: Comments use mini-Markdown formatting: [link](http://example.com) _italic_ boldcode. The post author will always be notified of your comment. To also notify a previous commenter, mention their user name: @peter or @PeterSmith will both work (no offence, but clicking help links should be common knowledge :))
[link](http://example.com)_italic_ boldcode. The post author will always be notified of your comment. To also notify a previous commenter, mention their user name: @peter or @PeterSmith will both work (no offence, but clicking help links should be common knowledge :))