Custom Tags and Javascript access to plain maps?

I’ve looked through the basic FAQ and other pages but can’t find any information on how I can create a custom tag that is suitable to my own project only. A tag that doesn’t get shown unless flagged to show.

Also I want to be able to display maps in a iframe on my website. How can I do this without displaying the other parts of the webpage. I want the map only. Is there any Javascript routines to manipulate maps?

Maybe I could overlay an image like a pin-icon on top of the map at my server and client-browser level, if I could display the map within the page, not an iframe source.

Thanks for any one that helps.

If you can add a tag to a node, way or relation then you can also make your own tag. I don’t understand the problem.

How to embed a slippy map (and other nice things):

Also see this page:
If you want a tag that would be useful for something, you can just make something up and start using it. That page has some guidelines for how to name/format your tag. And also worth documenting it on the wiki, so others can find out what it means.