advpack: Add documentation for ExtractFiles.

dlls/advpack/advpack.c

@@ -578,10 +578,31 @@ HRESULT WINAPI ExecuteCab( HWND hwnd, PCABINFO pCab, LPVOID pReserved )
 /***********************************************************************
  *             ExtractFiles    (ADVPACK.@)
  *
+ * Extracts the specified files from a cab archive into
+ * a destination directory.
+ *
+ * PARAMS
+ *   CabName   [I] Filename of the cab archive.
+ *   ExpandDir [I] Destination directory for the extracted files.
+ *   Flags     [I] Reserved.
+ *   FileList  [I] Optional list of files to extract.  See NOTES.
+ *   LReserved [I] Reserved.  Must be NULL.
+ *   Reserved  [I] Reserved.  Must be 0.
+ *
+ * RETURNS
+ *   Success: S_OK.
+ *   Failure: E_FAIL.
+ *
+ * NOTES
+ *   FileList is a colon-separated list of filenames.  If FileList is
+ *   non-NULL, only the files in the list will be extracted from the
+ *   cab file, otherwise all files will be extracted.  Any number of
+ *   spaces, tabs, or colons can be before or after the list, but
+ *   the list itself must only be separated by colons.
+ *
  * BUGS
- *   Unimplemented
+ *   Unimplemented.
  */
-
 HRESULT WINAPI ExtractFiles ( LPCSTR CabName, LPCSTR ExpandDir, DWORD Flags,
                               LPCSTR FileList, LPVOID LReserved, DWORD Reserved)
 {