Function known 

fn known(
    world: &World<'_>,
    consent: &Consent,
    uri: &str,
) -> Result<String, String>

An address as Sioul writes it, of something it knows: a message kept here, a task, a note…; or a web page (https://…). It is written into a task, an event or a note’s front matter as it is, so it is one line of visible characters; and the window opens it when the person clicks it, so it is never a file of this computer (file:) nor another program’s scheme (smb:, ms-…:). A thing kept from agents is refused: it is not tied to, whatever ties it.