ion at all, and in fact expands the data slightly to produce
the <em>zlib</em> format (it is not a byte-for-byte copy of the input).
More advanced applications of <em>zlib</em>
may use <tt>deflateInit2()</tt> here instead.  Such an application may want to reduce how
much memory will be used, at some price in compression.  Or it may need to request a
<em>gzip</em> header and trailer instead of a <em>zlib</em> header and trailer, or raw
encoding with no header or trailer at all.
<p>
We must check the return v