It is context of digital advertising is the method by which certain rich media ads are allowed to expand on a user’s screen, as well as some javascript-based technologies scrape information from the page.
For example, if a publisher wanted to enable an advertiser’s tag to expand from 300×250 to 600×500, and was using an iFrame to load ads asynchronously on their page, they would need to allow the advertiser’s tag to “break” the pre-set dimensions of their iFrame. Technically speaking though, because the rules on which Javascript was built does not allow two iFrames to talk to each other if they are from different domains – for example, a publisher domain and a 3rd party ad server domain – there isn’t a way for the 3rd party ad tag to tell the publisher’s page that it needs to serve an image larger than that of the iFrame.
So to address this problem, rich media vendors ask that publisher place a file in the publisher ad server’s subdomain. This file doesn’t really have a name in the ad tech world, some just call it a publisher file, others call it a bridge or gateway file, but all rich media companies have it. This file’s location must be known to the rich media vendor, and then what happens is when a rich media tag loads into that publisher’s iFrame, it quickly looks up that file (some javascript), sends some various parameters (things like the unique identifier for the ad that needs to serve) to the that file, which then makes another request to the rich media vendor. Basically, the 3rd party ad tag redirects itself through the publisher file so that the request appears to come from the publisher’s domain, because the javascript is hosted on the publisher’s domain. That solves the problem of allowing the iFrame to talk to the publisher’s page, and the iFrame is thereby allowed to expand.
Pointroll has a good explanation on their side, and an example file you can actually look at:https://wiki.pointroll.com/display/PRRC/iFrame+Delivery+Specs
Other technologies that want to bust iFrames are technologies like ad verification, which want to know the URL of the page they are serving on so they can report it back to an advertiser.A single or even two nested iFrames can be busted by various clever javascript coding to scrape information from the page,
Credits :Ben
