Setting the policy lets you list the URL patterns that specify which sites can't ask users to grant them read access to files or directories in the host operating system's file system via the File System API.
Leaving the policy unset means DefaultFileSystemReadGuardSetting applies for all sites, if it's set. If not, users' personal settings apply.
URL patterns can't conflict with FileSystemReadAskForUrls. Neither policy takes precedence if a URL matches with both.
For detailed information on valid url patterns, please see https://cloud.google.com/docs/chrome-enterprise/policies/url-patterns. * is not an accepted value for this policy.