Function share 

pub fn share(
    tasks: &[StoryTask<'_>],
    task: &str,
    scenarios: &[String],
    verified: &BTreeSet<String>,
    deferred: bool,
) -> Option<Share>

What judges task of the story tasks, whose scenarios are scenarios (in the story’s order), of which earlier ticks verified verified, and which a person deferred to the checkpoint when deferred. None: the story has no scenario, or the task is judged by its checks alone.

Links naming no scenario of the story are ignored (the plan reports them). The checkpoint comes first: a link never narrows what it judges.