This is pretty nit picky, but I guess this is what happens when people use a non-validating editor to edit their HTML. I know this isn't the point of the article but let's teach everything properly not just JavaScript techniques. It bugs me that after all these years people are still creating invalid HTML when there are so many tools out there, including the HTML validator: http://validator.w3.org/

An id is defined as follows:

id = name [CS]
This attribute assigns a name to an element. This name must be unique in a document.

Then if you dig further you will see that a "name" token is defined as follows:

ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

There are lots of other issues with this HTML, but you'll find those if you validate it. The id issue was just the most obvious one as it plays a primary part in the JavaScript itself.