function extendComment() {
	var lines = (this.value.match(/\n/g) || []).length + 3;
	this.rows = Math.max(7, Math.min(20, lines));
}

var events = ['keyup', 'keydown', 'keypress', 'blur', 'focus'];

Event.observe(window, 'DOMContentLoaded', function() {
	events.each(function(handler) {
		$$('#comment-form textarea')
			.invoke('observe', handler, extendComment);
	});
});