A Shopping Comparison Listing ad.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v26/common/ad_type_infos.proto)

| Fields ||
|---|---|
| ## `headline` | `string` Headline of the ad. This field is required. Allowed length is between 25 and 45 characters. |