 }
 
 extension Archive {
+    /// The number of the work units that have to be performed when
+    /// removing `entry` from the receiver.
+    ///
+    /// - Parameter entry: The entry that will be removed.
+    /// - Returns: The number of the work units.
     public func totalUnitCountForRemoving(_ entry: Entry) -> Int64 {
         return Int64(self.endOfCentralDirectoryRecord.offsetToStartOfCentralDirectory
                    - UInt32(entry.localSize))

        return Progress(totalUnitCount: self.totalUnitCountForReading(entry))
    }

    public func totalUnitCountForAddingItem(at url: URL) -> Int64 {
        var count = Int64(0)
        do {

        return Progress(totalUnitCount: self.totalUnitCountForRemoving(entry))
    }

    /// The number of the work units that have to be performed when
    /// reading `entry` from the receiver.
    ///
    /// - Parameter entry: The entry that will be read.
    /// - Returns: The number of the work units.
    public func totalUnitCountForReading(_ entry: Entry) -> Int64 {
        switch entry.type {
        case .file, .symlink:
