title: Adjust font size XSL-FO with Apache FOP
body: <p>I have the following Docbook 5.1 document</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;book xmlns="http://docbook.org/ns/docbook"
      xmlns:xlink="http://www.w3.org/1999/xlink"
      version="5.1"&gt;
      &lt;info&gt;
          &lt;title&gt;Test&lt;/title&gt;
      &lt;/info&gt;
      &lt;chapter&gt;
          &lt;title&gt;Switchs of &lt;systemitem class="domainname"&gt;corp.net&lt;/systemitem&gt;&lt;/title&gt;
          &lt;para&gt;
              Switchs: &lt;systemitem class="fqdomainname"&gt;switch-&lt;replaceable&gt;id&lt;/replaceable&gt;.corp.net&lt;/systemitem&gt;.
          &lt;/para&gt;
      &lt;/chapter&gt;
  &lt;/book&gt;
  </code></pre>
  
  <p>And I use the following customization stylesheet</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"&gt;
      &lt;xsl:import href="http://docbook.sourceforge.net/release/xsl-ns/current/fo/profile-docbook.xsl"/&gt;
      &lt;xsl:param name="monospace.font.family"&gt;Liberation Mono&lt;/xsl:param&gt;
      &lt;xsl:attribute-set name="monospace.properties"&gt;
          &lt;!-- XXX --&gt;
      &lt;/xsl:attribute-set&gt;
  &lt;/xsl:stylesheet&gt;
  </code></pre>
  
  <p>Unfortunately, the monospace font I use is too large, so I want to reduce
  it down to 85% of the serif font's size.</p>
  
  <p>The first thing I tried was</p>
  
  <pre><code>&lt;xsl:attribute name="font-size"&gt;0.85em&lt;/xsl:attribute&gt;
  </code></pre>
  
  <p>It worked well except when there is nested monospaced text. In this case, the inner one
  is too small.</p>
  
  <p>Then I tried</p>
  
  <pre><code>&lt;xsl:attribute name="font-size"&gt;
      &lt;xsl:value-of select="$body.font.master * 0.85"/&gt;
      &lt;xsl:text&gt;pt&lt;/xsl:text&gt;
  &lt;/xsl:attribute&gt;
  </code></pre>
  
  <p>It doesn't work when the monospaced text is "inside" a larger sized text (eg. titles).</p>
  
  <p>I've read <a href="http://docbook.sourceforge.net/release/xsl/1.78.1/doc/fo/monospace.properties.html" rel="nofollow noreferrer">http://docbook.sourceforge.net/release/xsl/1.78.1/doc/fo/monospace.properties.html</a>, that recommends to use <code>font-size-adjust</code>, but FOP 2.3 doesn't support it.</p>
  
  <p>Is there a way to simulate the <code>font-size-adjust</code> behavior ?</p>