         return exists(type: String(reflecting: type), name: nil, container: nil, metafilter: nil)
     }
     
+    /**
+     Returns true if any registrations exist matching the given metafilter, regardless of type, name, or container.
+    */
     public static func exists<M>(metafilter: @escaping Metafilter<M>) -> Bool {
         return exists(type: nil, name: nil, container: nil, metafilter: metathunk(metafilter))
     }

    }
    
    /**
     Returns true if there are any keys registered in the given container.
    */
    public static func exists<C: Hashable, M>(container: C, metafilter: @escaping Metafilter<M>) -> Bool {
        return exists(type: nil, name: nil, container: container, metafilter: metathunk(metafilter))

    /**
     Helper method for filtering.
     */
    private static func exists(type: String?, name: AnyHashable?, container: AnyHashable?, metafilter: Metathunk? = nil) -> Bool {
        return lock.read {
            for (key, dependency) in registrations {
                if let type = type, type != key.type { continue }
