Add missing documentation

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/dec/BrotliStream.Decompress.cs

@@ -96,7 +96,7 @@ public override int Read(Span<byte> buffer)
         /// <summary>Begins an asynchronous read operation. (Consider using the <see cref="System.IO.Stream.ReadAsync(byte[],int,int)" /> method instead.)</summary>
         /// <param name="buffer">The buffer from which data will be read.</param>
         /// <param name="offset">The byte offset in <paramref name="buffer" /> at which to begin reading data from the stream.</param>
-        /// <param name="count">To maximum number of bytes to read.</param>
+        /// <param name="count">The maximum number of bytes to read.</param>
         /// <param name="asyncCallback">An optional asynchronous callback, to be called when the read operation is complete.</param>
         /// <param name="asyncState">A user-provided object that distinguishes this particular asynchronous read request from other requests.</param>
         /// <returns>An object that represents the asynchronous read operation, which could still be pending.</returns>

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/enc/BrotliStream.Compress.cs

@@ -125,6 +125,10 @@ public override void EndWrite(IAsyncResult asyncResult) =>
         /// <param name="count">The maximum number of bytes to write.</param>
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is <see cref="System.Threading.CancellationToken.None" />.</param>
         /// <returns>A task that represents the asynchronous write operation.</returns>
+        /// <exception cref="System.ArgumentNullException"><paramref name="buffer" /> is <see langword="null" />.</exception>
+        /// <exception cref="System.ArgumentOutOfRangeException"><paramref name="offset" /> or <paramref name="count" /> is negative.</exception>
+        /// <exception cref="System.ArgumentException">The sum of <paramref name="offset" /> and <paramref name="count" /> is greater than the buffer length.</exception>
+        /// <exception cref="System.ObjectDisposedException">The write operation cannot be performed because the stream is closed.</exception>
         /// <remarks><para>This method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in apps where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working. The async methods are used in conjunction with the <see langword="async" /> and <see langword="await" /> keywords in Visual Basic and C#.</para>
         /// <para>Use the <see cref="System.IO.Compression.BrotliStream.CanWrite" /> property to determine whether the current instance supports writing.</para>
         /// <para>If the operation is canceled before it completes, the returned task contains the <see cref="System.Threading.Tasks.TaskStatus.Canceled" /> value for the <see cref="System.Threading.Tasks.Task.Status" /> property.</para></remarks>

src/libraries/System.IO.Compression/src/System/IO/Compression/CompressionMode.cs

@@ -3,9 +3,15 @@
 
 namespace System.IO.Compression
 {
+    /// <summary>
+    /// Specifies whether to compress or decompress the underlying stream.
+    /// </summary>
     public enum CompressionMode
     {
+        /// <summary>Decompresses the underlying stream.</summary>
         Decompress = 0,
+
+        /// <summary>Compresses the underlying stream.</summary>
         Compress = 1
     }
 }

src/libraries/System.IO.Compression/src/System/IO/Compression/ZipArchiveEntry.cs

@@ -214,6 +214,9 @@ internal ZipArchiveEntry(ZipArchive archive, string entryName)
         /// </summary>
         public ZipArchive Archive => _archive;
 
+        /// <summary>
+        /// Gets the CRC-32 checksum of the uncompressed entry data.
+        /// </summary>
         [CLSCompliant(false)]
         public uint Crc32 => _crc32;
 
@@ -270,6 +273,12 @@ public long CompressedLength
             }
         }
 
+        /// <summary>
+        /// Gets or sets the external file attributes of the entry, whose meaning depends on the platform
+        /// that created the archive (for example, Unix file mode bits or Windows file attributes).
+        /// </summary>
+        /// <exception cref="InvalidOperationException">The entry has been deleted from the archive.</exception>
+        /// <exception cref="ObjectDisposedException">The archive that the entry belongs to has been disposed.</exception>
         public int ExternalAttributes
         {
             get
@@ -510,6 +519,28 @@ public Stream Open(FileAccess access)
             return OpenCore(access);
         }
 
+        /// <summary>
+        /// Opens the entry for reading or updating with the specified access mode and password.
+        /// This allows for more granular control over the returned stream's capabilities.
+        /// If the entry is not encrypted, the password is ignored and the entry is opened normally.
+        /// </summary>
+        /// <param name="access">The file access mode for the returned stream.</param>
+        /// <param name="password">The password used to decrypt the entry. If the entry is not encrypted, this parameter is ignored.</param>
+        /// <returns>A <see cref="Stream"/> that represents the contents of the entry with the specified access capabilities.</returns>
+        /// <remarks>
+        /// <para>The allowed <paramref name="access"/> values depend on the <see cref="ZipArchiveMode"/>:</para>
+        /// <list type="bullet">
+        /// <item><description><see cref="ZipArchiveMode.Read"/>: Only <see cref="FileAccess.Read"/> is allowed.</description></item>
+        /// <item><description><see cref="ZipArchiveMode.Create"/>: <see cref="FileAccess.Write"/> and <see cref="FileAccess.ReadWrite"/> are allowed (both write-only).</description></item>
+        /// <item><description><see cref="ZipArchiveMode.Update"/>: All values are allowed. <see cref="FileAccess.Read"/> provides a read-only stream over the entry's current content, including any modifications made in the current session. <see cref="FileAccess.Write"/> discards existing content and provides an empty writable stream. <see cref="FileAccess.ReadWrite"/> loads existing content into memory (equivalent to <see cref="Open(ReadOnlySpan{char})"/>).</description></item>
+        /// </list>
+        /// </remarks>
+        /// <exception cref="ArgumentOutOfRangeException"><paramref name="access"/> is not a valid <see cref="FileAccess"/> value.</exception>
+        /// <exception cref="ArgumentException">The entry is encrypted and <paramref name="password"/> is empty.</exception>
+        /// <exception cref="InvalidOperationException">The requested access is not compatible with the archive's open mode.</exception>
+        /// <exception cref="IOException">The entry is already currently open for writing. -or- The entry has been deleted from the archive. -or- The archive that this entry belongs to was opened in ZipArchiveMode.Create, and this entry has already been written to once.</exception>
+        /// <exception cref="InvalidDataException">The entry is missing from the archive or is corrupt and cannot be read. -or- The entry has been compressed using a compression method that is not supported.</exception>
+        /// <exception cref="ObjectDisposedException">The ZipArchive that this entry belongs to has been disposed.</exception>
         public Stream Open(FileAccess access, ReadOnlySpan<char> password)
         {
             ThrowIfInvalidArchive();