Explain effect of LZMA2_DIC_SIZE_FROM_PRO, also mentioned in lzma-spe…

…cification.txt from the SDK, and seen in test (especially when compressing).

ISHelp/isetup.xml

@@ -4454,7 +4454,7 @@ Name: portablemode; Description: "Portable Mode"</pre></example>
 </table>
 <p>The compression memory requirements are approximately 60% of the above when <link topic="setup_lzmamatchfinder">LZMAMatchFinder</link> is set to <tt>HC</tt> at the expense of compression ratio.</p>
 </indent>
-<p><tt>lzma2</tt> is the method of compression employed by the <extlink href="http://www.7-zip.org/">7-Zip LZMA2</extlink> compressor. LZMA2 is a modified version of LZMA that offers a better compression ratio for incompressible data (random data expands about 0.005%, compared to 1.35% with original LZMA), and optionally can compress multiple parts of large files in parallel, greatly increasing compression speed but with a possible reduction in compression ratio (see <link topic="setup_lzmanumblockthreads">LZMANumBlockThreads</link>). Like LZMA, it can consume a <i>lot</i> of memory; see the above table. If a compression level isn't specified, it defaults to <tt>max</tt>.</p>
+<p><tt>lzma2</tt> is the method of compression employed by the <extlink href="http://www.7-zip.org/">7-Zip LZMA2</extlink> compressor. LZMA2 is a modified version of LZMA that offers a better compression ratio for incompressible data (random data expands about 0.005%, compared to 1.35% with original LZMA), and optionally can compress multiple parts of large files in parallel, greatly increasing compression speed but with a possible reduction in compression ratio (see <link topic="setup_lzmanumblockthreads">LZMANumBlockThreads</link>). If a compression level isn't specified, it defaults to <tt>max</tt>. Like LZMA, LZMA2 can consume a <i>lot</i> of memory; see the above table. Do note: LZMA2 only supports a limited number of dictionary sizes and other sizes will be rounded up to the next supported size. Supported sizes are powers of two starting at 4 (4, 8, 16, 32, etc., up to 1048576) and the midway points between them (6, 12, 24, etc., up to 786432). For instance, a dictionary size of 524289 (512 MB + 1 byte) has the same memory requirements as one of 786432 (768 MB).</p>
 <p><tt>none</tt> specifies that no compression be used.</p>
 <p><b>See also:</b><br/>
 <link topic="setup_solidcompression">SolidCompression</link><br/>