Is there an \"invisible\" tag in HTML (4) that I can use to make CSS distinctions
tag.myclass tag.mysubclass h1 { }
without having
No, there is not.
(And that's because such an element wouldn't really fit into the rest of HTML. The only reason DIV and SPAN affect the surrounding area is because they're block and inline elements, respectively. What would an 'invisible' element be? If you need something that's completely independent, absolutely (or relatively) position it and give it a higher z-index.)