How to store arbitrary data for some HTML tags

Which version of HTML are you using?

In HTML 5, it is totally valid to have custom attributes prefixed with data-, e.g.

<div data-internalid="1337"></div>

In XHTML, this is not really valid. If you are in XHTML 1.1 mode, the browser will probably complain about it, but in 1.0 mode, most browsers will just silently ignore it.

If I were you, I would follow the script based approach. You could make it automatically generated on server side so that it's not a pain in the back to maintain.

If you are using jQuery already then you should leverage the "data" method which is the recommended method for storing arbitrary data on a dom element with jQuery.

To store something:

$('#myElId').data('nameYourData', { foo: 'bar' });

To retrieve data:

var myData = $('#myElId').data('nameYourData');

That is all that there is to it but take a look at the jQuery documentation for more info/examples.