Document：featurePolicy 属性
Deprecated
Avoid using this feature in new projects. Feature policy is superseded by permissions policy. This feature may be a candidate for removal from web standards or browsers.
Consider using the following features instead: Permissions policy.
Document 接口的 featurePolicy 只读属性返回 FeaturePolicy 接口，该接口提供了用于检查应用于特定文档的权限策略的简单 API。