A student reports this problem when using HTML and JavaScript: This assignment has been nothing but trouble. I had some problems getting things to display correctly in both IE and Firefox and having...

A student reports this problem when using HTML and JavaScript: “This assignment has been nothing but trouble. I had some problems getting things to display correctly in both IE and Firefox and having things disappear when I clicked an option button. The Web site resource has helped a little but has mostly been a headache.” What kind of error is it? What rules were applied, and which should have been applied earlier?