Types of zone tags
A zone tag is a snippet of code that places your ad item on a publisher's webpage or app. It passes along information about the ad item, and usually other details such as ones needed to track the ad's performance.
Choosing the right type of zone tag is important because your ad item may not show or you may miss some features if you didn't use the appropriate zone tag for your needs or restrictions.
Asynchronous 1.1 (Beta)
document.write method of drawing to the page. Instead, the Async Beta tag will render directly to the placement container DIV.
This is particularly useful in cases like infinitely scrolling sites where
document.write may cause conflicts with white pages or empty spots.
This zone tag is synchronous, meaning it will ask the webpage to wait for the ad to load before loading the rest of the page's contents. Normally this delay is so small that it doesn't affect the website visitor or app user's experience. But if a zone is set for programmatic bidding, the delay will usually be compounded, leading to a noticeable delay in loading time. We recommend using Async tags for such zones.
iFrame & iFrame (HTML Only)
iFrame tags load content securely and are unable to interact with the page it is displayed on. iFrames also load asynchronously.
This is an HTML image tag wrapped in a hyperlink tag to direct users when they click on the ad.
JSON Ad API
We recommend this zone tag only if you want to heavily customize when or how your ad is rendered because they add more steps to the process compared to other zone tags. That being said, their flexibility may be worth it for your needs.
These tags are lightweight, easy to use, and are AMP-compliant, allowing mobile sites to load as quickly as possible. There are two cases where you'll have to modify your AMP tags before they can serve, which you can read about here.