What happens if you included an iframe that contained a meta noindex tag?
Meta tags are not in the rendered html, and therefore would have no influence over the main page. However, it looks like the content of the iframe is not included. So noindex could be a way of excluding parts of a page from indexing. The preview tool contradicts that, as it does show the content of the iframe (maybe a bug?). Early tests indicate the content in a noindex iframe does not show in search results.