Does anyone know the do's and don't of commenting in FireFox 3.x?

Question

I decided to show a breaking version of what I am talking about. It is not important how it messes up the layout, only that it causes the DIV element to be null....

 <!-- [ top panel ] --><div id="top_panel">
 <!-- -------------------------------------- -->
    <script type="text/javascript">
   alert(document.getElementById('top_panel'));
    </script>
 </div>

The above code will return the element as null, every time.... if I increase or decrease the number of dashes it still fails as long as the interior dashes end with a closing pair of dashes. For the sake of example, I will use [open] and [close] to represent pairs of "--" dashes...

So, the code ends up being interpreted this way to break:

 <!-- [close][open][close][open][close][open][close][open][close] -->

In this example, it is the last [close] and the "-->" which now cause an open, hanging comment.

I only seem to run into comment-based issues in FF these days. All other browsers seem okay with anything I have thrown at them...

I KNOW that this is not considered legal commenting, but it still does not change the fact that I had to trip over this situation to become aware of the issue... I am hoping others can avoid the same simple problem and share their own twists on weird, comment-based issues in any browser... I am sure this is not the only instance of good commenting gone bad.

I also understand that leaving a space after the "<" is a no-no as well: "<" + " " + "!" + "--" = Nooooo!

Thanks for all your help, all!

Answer 1

You can't use -- inside comments because it ends the comment. This isn't a Firefox thing - it's defined by the standards. Any browser that doesn't treat -- as start/end of comment is doing it wrong and most likely will be bug-fixed eventually.

White space is not permitted between the markup declaration open delimiter("<!") and the comment open delimiter ("--"), but is permitted between the comment close delimiter ("--") and the markup declaration close delimiter (">"). A common error is to include a string of hyphens ("---") within a comment. Authors should avoid putting two or more adjacent hyphens inside comments.

Answer 2

Are you serving XHTML? According to the XML standard,

For compatibility, the string " -- " (double-hyphen) MUST NOT occur within comments.

Edit: the same restriction exists in regular HTML, too.