Not really I think. This is basically my 2nd solution.Based on some criterion I want to show 0, 1, or some of the <tr>s.The criterion is something which should not show on the screen, but is part of the <tr>.In my 2nd solution I indeed do use innerHTML to get the string"<!-- id="a" -->...."Then I extract with some substring-guru-stuff the "a" or "b" to decide whether to show or hide the <tr>. But this depends on the exact layout of the comment.What I want to do is something like:<table><tr userdata="a">...</tr><tr userdata="a">...</tr><tr userdata="b">...</tr>...</table>But thats not HTML The nearest to that is using the id attribute, see solution 1).But that's (I think) mis-using the id attribute.So I wonder if there's a general way to add some user-defined attribute to an element (any element, not just <tr>, btw) that does not influence HTML in any way, but that can be extracted in JavaScript using the DOM...The Dutch word 'dom' means 'stupid', btw Thanks for bearing with me....Martijn