Allows you to register a list of protocol handlers. This can only be a recommended policy. The property |protocol| should be set to the scheme such as 'mailto' and the property |url| should be set to the URL pattern of the application that handles the scheme. The pattern can include a '%s', which if present will be replaced by the handled URL.
The protocol handlers registered by policy are merged with the ones registered by the user and both are available for use. The user can override the protocol handlers installed by policy by installing a new default handler, but cannot remove a protocol handler registered by policy.