Constant RESOURCE_LINK_SCHEME 

pub const RESOURCE_LINK_SCHEME: &'static str;

The scheme a resource link is written with in a link mark’s target, in the one form every document codec already round-trips: tilo://open#…, the native link tilo_reference::link::Link::to_native makes. A link mark whose target starts with this scheme names a resource, so it is shown as a Mark::ResourceLink rather than an external URL.