Considering the removal of <iframe seamless> on issue #331.

For me, the main feature of @seamless was the ability for the iframe to resize based on the size of the child document (really just the height), so no scroll bars would appear.

Currently this is "solved" with the use of some very messy JavaScript:

http://stackoverflow.com/search?q=resize+iframe

Which is more difficult cross-origin, which needs postMessage and custom JS running on every single page (both child and parent).

The suggestion of Shadow-DOM is interesting, but I don't believe this provides the same level of protection (and backwards compatibility), as often the child content is put in an iframe to keep it isolated from the current page (i.e. for security reasons).

Typically I put things in an iframe because they could easily be malicious, and I would really like to use a sandbox to block allow-scripts.