regex for multiple line breakes

Hi there, I am trying to remove multiple linebreakes from a textarea input. Spammers tend to insert multiple line breakes. The problem is, that I want to allow 2 line breaks so basic formating should be allowed. I am doing this by regex: $data[txt] = preg_replace('[\r\n]+',"\n",$data[txt]); I would need a regex that allows \r\n\r\n, but not more than this. Thank you for any help, Merlin