pub fn get_head(&self, url: &PathMaybeWithLocale) -> Option<String> {
        let map = self.map.borrow();
        match map.get(url) {
            Some(entry) => entry.head.as_ref().map(|v| v.to_string()),
            None => None,
        }
    }
Gets the document metadata registered for a URL, if it exists.
packages/perseus/src/state/state_store.rs