pub fn contains(&self, url: &PathMaybeWithLocale) -> PssContains {
        let map = self.map.borrow();
        let contains = match map.get(url) {
            Some(entry) => match entry.state {
                PssState::Some(_) => match entry.head {
                    Some(_) => PssContains::All,
                    None => PssContains::State,
                },
                PssState::None => match entry.head {
                    Some(_) => PssContains::Head,
                    None => PssContains::None,
                },
                PssState::Never => match entry.head {
                    Some(_) => PssContains::HeadNoState,
                    None => PssContains::None,
                },
            },
            None => PssContains::None,
        };
        // Now do a final check to make sure it hasn't been preloaded (which would show
        // up as `PssContains::None` after that)
        match contains {
            PssContains::None | PssContains::Head | PssContains::State => {
                let preloaded = self.preloaded.borrow();
                let route_preloaded = self.route_preloaded.borrow();
                // We don't currently distinguish between *how* the page has been preloaded
                if route_preloaded.contains_key(url) || preloaded.contains_key(url) {
                    PssContains::Preloaded
                } else {
                    contains
                }
            }
            _ => contains,
        }
    }
Checks if the state contains an entry for the given URL.
packages/perseus/src/state/state_store.rs