What MUST be included in an HTML5 ad to ensure proper functionality?

In an HTML5 ad, including a click tag is essential for ensuring the ad's interactivity functions correctly. The click tag serves as a way to define a URL that users will be directed to when they click on the advertisement. This is crucial for tracking user engagement and ensuring that the ad leads to the intended destination, such as a landing page or website related to the ad content.

The click tag is a JavaScript variable that developers use within the ad’s code to capture click events. Without it, the advertisement would not properly register user interactions, which is a key component of digital advertising. Therefore, its inclusion is necessary to meet both functionality and reporting requirements in ad campaigns.

Other components like tracking pixels, ad serving code, and style sheets may enhance the ad's capabilities or presentation, but they are not strictly required for the fundamental interactive element that the click tag provides.