Function render_in 

pub async fn render_in<B: Backend>(
    session: &mut Session,
    graph: &Graph,
    target: &str,
    config: RenderConfig,
    tier: &Tier<B>,
    abandon: &dyn Abandon,
) -> Result<Render, EngineError>

target over tier, from the root down, typed anew only where session typed it otherwise; a node memory answers stands as its samples. With out dropped and no reading, a root it answers ends the render unread. Abandoned, it stops before its next block.