+@node Decompression
+@section Dealing With Compressed Data
+
+When @code{auto-compression-mode} is enabled, Emacs automatically
+uncompresses compressed files when you visit them, and automatically
+recompresses them if you alter and save them. @xref{Compressed
+Files,,, emacs, The GNU Emacs Manual}.
+
+The above feature works by calling an external executable (e.g.,
+@command{gzip}). Emacs can also be compiled with support for built-in
+decompression using the zlib library, which is faster than calling an
+external program.
+
+@defun zlib-available-p
+This function returns non-@code{nil} if built-in zlib decompression is
+available.
+@end defun
+
+@defun zlib-decompress-region start end
+This function decompresses the region between @var{start} and
+@var{end}, using built-in zlib decompression. The region should
+contain data that were compressed with gzip or zlib. On success, the
+function replaces the contents of the region with the decompressed
+data. On failure, the function leaves the region unchanged and
+returns @code{nil}. This function can be called only in unibyte
+buffers.
+@end defun
+
+