Anyone ever use -i settingsFileIn of security add-trusted-cert?

Hi,
Does anyone have any experience with the settingsFileIn (-i option) of the security add-trusted-ert framework?
ie.:
security add-trusted-cert -d -r trustAsRoot -k blah.keychain /tmp/cert.pem -i settings.plist

Or, does anyone have any documentation on the format of the plist file so that you could actually create settings and import them?

Apple seems to have published nothing on this.

Thanks!