path: root/src/documentation/content/xdocs/dev/faq.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE faqs PUBLIC "-//APACHE//DTD FAQ V1.1//EN" "dtd/faq-v11.dtd">
<faqs title="FOP FAQ">
  <part>
    <title>General questions</title>
    <faq>
      <question>What is FOP?</question>
      <answer>
      <p>
        FOP is a print formatter for <jump href="#XSLFO">XSL formatting
        objects</jump>.
      </p>
      <p>
        It can be used to render an XML file containing XSL formatting objects
        into a page layout. The main target is PDF but other rendering targets
        are supported, such as AWT, PCL, text and direct printing.
      </p>
      </answer>
    </faq>
    <faq>
      <question>What can I do with FOP?</question>
      <answer>
        <p>
          FOP provides both an application and a library that converts an XSL FO
          document into paginated output.
        </p>
        <p>
          The FOP command line application can be directly used to transform XML
          into PDF, PostScript, PCL and other formats, there is also an AWT
          based viewer integrated.
        </p>
        <p>
          The library can be used in servlets and other Java applications.
        </p>
      </answer>
    </faq>
    <faq>
      <question>What does "FOP" stand for?</question>
      <answer>
        <p>
          It's an acronym for <strong>F</strong>ormatting
          <strong>O</strong>bject <strong>P</strong>rocessor
        </p>
      </answer>
    </faq>
    <faq>
      <question>How does FOP interact with other Apache Projects?</question>
      <answer>
        <p>
          FOP is distributed with <link
          href="http://xml.apache.org/cocoon">Cocoon</link> as a PDF serializer
          for XSL (FO) documents.
        </p>
        <p>
          <link href="http://xml.apache.org/batik">Batik</link> can be used with
          FOP to <link
          href="http://xml.apache.org/batik/svgrasterizer.html">transcode an SVG
          image</link> into a PDF document.
        </p>
      </answer>
    </faq>
    <faq>
      <question>What is XSL?</question>
      <answer>
        <p>
          XSL is a W3C standard concerned with publishing XML documents. It
          consists of two parts: <jump href="#XSLT">XSLT</jump> and <jump
          href="#XSLFO">XSLFO</jump>. The acronym expands to
          e<strong>X</strong>tensible <strong>S</strong>tylesheet
          <strong>L</strong>anguage.
        </p>
      </answer>
    </faq>
    <faq id="XSLFO">
      <question>What is XSLFO?</question>
      <answer>
        <p>
          XSLFO is an XML vocabulary that is used to specify a pagination and
          other styling for page layout output. The acronym &ldquo;FO&rdquo; stands for
          <strong>F</strong>ormatting <strong>O</strong>bjects. XSLFO can be
          used in conjunction with <jump href="#XSLT">XSLT</jump> to convert
          from any XML format into a paginated layout ready for printing or
          displaying.
        </p>
        <p>
          XSLFO defines a set of elements in XML that describes the way pages
          are set up. The contents of the pages are filled from flows. There can
          be static flows that appear on every page (for headers and footers)
          and the main flow which fills the body of the page.
        </p>
        <p>
          Synonyms: XSL FO, XSL (FO), XSL:FO, XSL-FO, Formatting Objects
        </p>
      </answer>
    </faq>
    <faq id="XSLT">
      <question>What is XSLT?</question>
      <answer>
        <p>
          XSLT describes the transformation of arbitrary XML input into other
          XML (like XSLFO), HTML or plain text. The &ldquo;T&rdquo; comes from
          <strong>T</strong>ransformation. For historical reasons, a
          transformation is often also called a &ldquo;style sheet&rdquo;.
        </p>
        <p>
          Synonyms: XSL transformation, XSL:T, XSL style sheet.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How can I contribute?</question>
      <answer>
        <p>
          There is always plenty of things to do. See <link>limitations</link>
          and <link>bugzilla</link>.
        </p>
      </answer>
    </faq>
  </part>
  <part>
    <title>Common stumbling blocks</title>
    <faq>
      <question>I get the error: [ERROR]: 'master-reference' for
      'fo:page-sequence'matches no 'simple-page-master' or
      'page-sequence-master'</question>
      <answer>
        <p>
          FOP was changed to be in accordance with the latest standard
          (see <link href="resources.html#w3-xsl">XSL
          standard</link>).The page master for a fo:page-sequence is
          now refereced by the master-reference attribute. Replace the
          master-name attributes of your fo:page-sequence elements by
          master-reference attributes. You have to do this also for
          fo:single-page-master-reference,
          fo:repeatable-page-master-reference and
          fo:conditional-page-master-reference elements in you page
          master definitions.
        </p>
        <p>
          See also <link>release notes</link>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>My PNG images don't work.</question>
      <answer>
        <p>
          The Jimi image library, which is used for processing images in PNG and
          other formats, was removed from the distribution for licensing
          reasons. You have to <fork href="http://java.sun.com">download</fork>
          and <link>install</link> it by yourself.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I get a NoClassDefFound exception.</question>
      <answer>
        <p>This is typically a problem with your <link>classpath</link>.</p>
        <p>If you are running FOP from the command line:</p>
        <ul>
          <li>
            Use the fop.bat or fop.sh command file from the FOP distribution.
            Ensure the directory where FOP and these files have been installed
            is the current working directory.
          </li>
          <li>
            If this doesn't help, check whether still all the jar files
            mentioned in the classpath in the fop.bat file are in their
            respective places.
          </li>
        </ul>
        <p>
          If you run FOP embedded in your servlet, web application or other Java
          application, check the classpath of the application.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I get a NoSuchMethodException or a NoSuchFieldException
      exception.</question>
      <answer>
        <p>
          This is usually caused by an older version of one of the FOP jars or
          old XML tools in the classpath. Check in particular for parser.jar,
          jaxp.jar, xml4j.jar or lotusxsl.jar.
        </p>
        <p>
          Incompatible versions of Batik may also cause this problem. Use
          the version of Batik that comes with FOP.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I get an OutOfMemoryException.</question>
      <answer>
        <p>
          FOP can consume quite a bit of memory, even though this has been
          continually improved. The memory consumption is partially inherent to
          the formatting process and partially caused by implementation
          choices. For certain layouts, all FO processors currently on the
          market have memory problems.
        </p>
        <p>
          Some hints regarding your document structure:
        </p>
        <ul>
          <li>
            Avoid forward <link>references</link>. Forward references cause all
            pages from the page with the reference on to be held in memory until
            the page with the referenced element is encountered. Common forward
            references are table of contents at the beginning of the document
            and the <link>"page N of TOTAL"</link> in footers. Forward
            references may be required by the task, however, if you are getting
            a memory overflow you should at least check whether this is really
            as necessary as claimed. A TOC, for example, could often be placed
            at the end of the document without dimishing it's value too much,
            the paper can be reshuffled after printing, and you can use
            bookmarks in PDF.
          </li>
          <li>
            Avoid large images, especially if they are scaled down. Scale them
            outside of FOP and use the already scaled images for the FOP
            run. For many image formats it is mainly the size of the image file
            which matters, not width*height, so you can try other means like
            using a higher compression rate.
          </li>
          <li>
            Use multiple page sequences. FOP starts rendering after the end of a
            page sequence is encountered. While the actual rendering is done
            page by page, some memory allocated for other purposes could
            possibly be freed after the page sequence has been rendered.
          </li>
          <li>
            Increase <link>memory settings of the JVM</link>. Be aware that it
            is usually unwise to increase the memory allocated to the JVM beyond
            the amount of physical RAM, it will significantly slow down. YMMV.
          </li>
        </ul>
        <p>
          There are also some bugs which cause FOP to go into an nonterminating
          loop, which also often results in a memory overflow. A characteristic
          symptom are continuous <jump href="#boxoverflow">box
          overflows</jump>. Most of them are triggered by elements not fitting
          in the available space, like big images and improperly specified width
          of nested block elements. Look for such stuff and correct it.
        </p>
        <p>
          Reducing memory consumption in general and squishing bugs is an
          ongoing effort, partially addressed in the <link>redesign</link>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I get a MalformedURLException.</question>
      <answer>
        <p>
          What you probably think of as "file names" are usually URLs, in
          particular the src attribute of fo:external-graphic.
        </p>
        <p>
          Because usage of URLs is growing, you should make yourself familiar
          with it. The relevant specification is <link
          href="http://www.rfc-editor.org/rfc/rfc2396.txt">RFC 2396</link>.
        </p>
        <p>
          In a nutshell, the correct syntax for an absolute file URL is
          <code>file:///some/path/file.ext</code> on Unix and
          <code>file:///z:/some/path/file.ext</code> on Windows systems. Note
          the triple slash, and also that only forward slashes are used, even on
          windows.
        </p>
        <p>
          A relative file URL starts with anything but a slash, and doesn't have
          the <code>file:</code> prefix, for example <code>file.ext</code>,
          <code>path/file.ext</code> or <code>../file.ext</code>. The string
          <code>file:path/file.ext</code> is <em>not</em> a relative URL,
          in fact, it isn't a valid URL at all. A relative URL is subject to a
          <link>resolving process</link>, which transforms it into an absolute
          URL.
        </p>
        <p>
          See <link>Understanding URIs and URLs</link> and <link>Understanding
          URL resolving</link>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I get an "[ERROR]: null", or a NullPointerException.</question>
      <answer>
        <p>
          Most often, you supplied an invalid FO document to FOP. Currently only
          very common errors are intercepted and produce a comprehensible error
          message. If you forgot container elements like fo:page-sequence or
          fo:flow and put blocks and inline elements directly as children of
          fo:root or fo:page-sequence, you'll only get a
          NullPointerException. Check whether your FO file has a proper
          structure. In some cases there are mandatory properties, like the
          master-reference in fo:conditional-page-master-reference, check also
          whether you got them right.
        </p>
        <p>
          You can use the <link>FOP DTD</link> or <link>FOP Schema</link> to
          validate your soure. This will catch most, but still not all problems.
        </p>
        <p>
          If you use XSLT, problems in your style sheet and in your source XML
          also often produce a NullPointerException. Run the transformation
          separately to check for this, usually you'll get a detailed error
          message from the XSLT processor.
        </p>
        <p>
          If you turn on debugging with the "-d" option you may be able to
          see more detailed information.
        </p>
      </answer>
    </faq>
    <faq>
      <question>FOP hangs. FOP does not exit.</question>
      <answer>
        <p>
          The most likely reason is a known problem with the Java run time
          environment which is triggered by rendering SVGs. Suns JDK 1.4 does
          not have this problem. See also <jump href="#svghangs">FOP does not
          exit if a SVG is included</jump>.
        </p>
        <p>
          Another possibility is that FOP went into a non terminating
          loop. Usually this is indicated by lots of log messages of the form
          "[INFO]: [NNNN]" which indicate a new page has been started or <jump
          href="#boxoverflow">box overflows</jump>. After some time, FOP will
          crash with an OutOfMemoryException.
        </p>
        <p>
          If you called the FOP command line application from some other
          programm, for example from Java using Runtime.exec(), it may hang
          while trying to write log entries to the output pipe. You have to read
          the FOP output regularly to empty the pipe buffer. It is best to avoid
          exec'ing FOP, use the library interface.
        </p>
      </answer>
    </faq>
    <faq id="boxoverflow">
      <question>FOP runs forever, writing lots of ">" to the log.</question>
      <answer>
        <p>
          There is something too large to fit into the intended place, usually a
          large image, a table whose rows are kept together or a block with a
          space-before or space-after larger than the page size. Catch the first
          page showing this phenomenon and check it. If it is not obvious which
          element causes the trouble, remove stuff until the problem goes
          away. Decrease the dimensions of the offending element or property, or
          increase the dimension of the enclosing element or container, or
          remove keep-with-* properties.
        </p>
      </answer>
    </faq>
    <faq>
      <question>FOP cannot find a file for fo:external-graphics.</question>
      <answer>
        <p>
          The src attribute of the fo:external-graphics element takes an URI,
          not a file name.
        </p>
        <p>
          Relative URLs are resolved against the baseDir property of FOP. For
          the command line FOP application, the baseDir is the directory of the
          input file, either the FO file or the XML source. If FOP is used
          embedded in a servlet, <link>baseDir can be set explicitely</link>. If
          it's not set, it is usually the current working directory of the
          process which runs FOP.
        </p>
        <p>
          See <link>Understanding URIs and URLs</link> and <link>Understanding
          URL resolving</link>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>FOP does not find my fonts.</question>
      <answer>
        <p>
          Did you get: &laquo;Failed to read font metrics file C:\foo\arial.xml
          : File "C:\foo\arial.xml" not found&raquo;? The value for the
          metrics-file attribute in the user config file is actually an URL, not
          a file name. Use "file:///C:/foo/arial.xml" instead.
        </p>
        <p>
          If you used a relative URL, make sure your application has the working
          directory you expect. Currently FOP does not use the baseDir for
          resolving relative URLs pointing to font metric files.
        </p>
      </answer>
    </faq>
    <faq>
      <question>Keep-with-next, keep-with-previous, keep-together
      don't work.</question>
      <answer>
        <p>
          These properties are not implemented, except for keep-with-next and
          keep-with-previous on table rows. In order to take advantage of them,
          you have to nest stuff to be kept together in a table.
        </p>
        <p>
          The concept is called &ldquo;blind table&rdquo;. The table is used for
          pure layout reasons and not obvious in the output.
        </p>
        <p>
          An example of an image and the image caption to be kept together:
        </p>
        <source><![CDATA[<fo:table table-layout="fixed" width="100%">
  <fo:table-column column-width="proportional-column-width(1)"/>
    <fo:table-body>
      <fo:table-row keep-with-next="always">
        <fo:table-cell>
          <fo:block>
            <fo:external-graphic src="foo.jpg"/>
          </fo:block>
        </fo:table-cell>
      </fo:table-row>
      <fo:table-row>
        <fo:table-cell>
          <fo:block>Image Caption</fo:block>
        </fo:table-cell>
      </fo:table-row>
    </fo:table-body>
  </fo:table>]]></source>
      </answer>
    </faq>
    <faq>
      <question>My tables are missing, or missing their content.</question>
      <answer>
        <p>
          Check for fo:table-body around the rows. FOP doesn't raise an error if
          it is omitted, it just drops the content.
        </p>
        <p>
          Also, the fo:table-with-caption element is not implemented, tables
          within such an element are dropped too. The DocBook style sheets
          generate fo:table-with-caption elements, so watch out.
        </p>
      </answer>
    </faq>
    <faq>
      <question>Text overflowing table cells and the like is not clipped. Long text
        flows into adjacent cells/block, obscuring stuff there.</question>
      <answer>
        <p>
          Clipping as specified by the <code>overflow="hidden"</code> is not yet
          implemented.  If you have long words overflowing table cells, try to
          get them hyphenated. Artificial names like product identifications or
          long numbers usually aren't hyphenated. You can try special processing
          at XSLT level, like
        </p>
        <ul>
          <li>
            clip long text,
          </li>
          <li>
            explicit wrapping+clipping,
          </li>
          <li>
            insert zero width spaces (U+200B or &amp;#x200B;) to allow FOP to
            wrap.
          </li>
        </ul>
        <p>
          Check the <link href="http://dpawson.co.uk/xsl">XSL FAQ</link> and the
          <link href="http://www.mulberrytech.com/xsl/xsl-list/">XSL list
          archive</link> for how to perform these tasks.
        </p>
      </answer>
    </faq>
    <faq>
      <question>Page numbers are not properly right aligned.</question>
      <answer>
        <p>
          This happens for fo:page-number-citation elements if the citation
          occurs before FOP formatted the requested page, usually in TOC or
          index pages.
        </p>
        <p>
          It is caused by the problem that FOP has to guess how much space the
          yet unknown page number will occupy, and usually the guesses are
          somewhat off. You can try to use a non-proportional font like Courier
          to remedy this. However, this is likely to look ugly, and wont fix the
          problem completely.
        </p>
      </answer>
    </faq>
    <faq>
      <question>A graphic is not displayed.</question>
      <answer>
        <p>
          Several possibilities:
        </p>
        <ul>
          <li>
            The graphic is too large to fit into the intended space.
          </li>
          <li>
            Some image format subclasses can't be handled, try to convert the
            graphic to a format subclass known to work. (Sorry, no list of
            formats known to work)
          </li>
          <li>
            Something else obscures the graphic, for example stuff from a static
            content (very rare, but has happened).
          </li>
        </ul>
        <p>
          See also <link>supported image formats</link>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>Hyphenation does not work.</question>
      <answer>
        <p>
          Set the language attribute somewhere. Check whether you use a language
          for which hyphenation is supported. Supported languages can be deduced
          from the files in the hyph directory of the FOP source distribution.
        </p>
      </answer>
    </faq>
  </part>
  <part>
    <title>Embedding FOP. Using FOP in a servlet</title>
    <faq>
      <question>How do I use FOP in a servlet?</question>
      <answer>
        <p>Look at the <link>servlet example</link>.</p>
        <p>
          A rather minimal code snippet to demonstrate the basics:
        </p>
        <source>response.setContentType("application/pdf");
Driver driver=new Driver( new InputSource("foo.fo"),
                          response.getOutputStream());
driver.setRenderer(Driver.RENDER_PDF);
driver.run();</source>
        <p>
          Caveat: Internet Explorer will not automatically show the PDF. Thats a
          well known IEx problem, not with the servlet. You can download the PDF
          with IEx and view it later. There are other problems with this code.
        </p>
        <p>
          Please look into <link>Howto embed FOP in a servlet</link> for all
          kinds of details.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How do I use FOP in a servlet with an XSLT transformation?</question>
      <answer>
        <p>
          Use the TraxInputHandler if both the source XML and XSL are read from
          files.
        </p>
        <p>
          A demonstration:
        </p>
        <source>response.setContentType("application/pdf");
XSLTInputHandler input
  =new XSLTInputHandler(new File("foo.xml"), new File("foo.xsl"));
Driver driver=new Driver();
driver.setOutputStream(response.getOutputStream());
driver.setRenderer(Driver.RENDER_PDF);
driver.render(input.getParser(), input.getInputSource());</source>
        <p>
          This minimal code snippet has the same problems as the one from the
          question above. Please inform yourself about the details.
        </p>
        <p>
          If your source XML is generated on the fly, for example from a
          database, a web service, or another servlet, you have to create a
          transformer object explicitely and use a SAX event stream to feed the
          transformation result into FOP.
        </p>
        <p>
          A demonstration:
        </p>
        <source>response.setContentType("application/pdf");
Driver driver =new Driver();
driver.setOutputStream(response.getOutputStream());
driver.setRenderer(Driver.RENDER_PDF);
Transformer transformer=TransformerFactory.newInstance()
        .newTransformer(new StreamSource("foo.xsl"));
transformer.transform(xmlsource, new SAXResult(driver.getContentHandler()));</source>
        <p>
         You don't have to call run() or render() on the driver object.
        </p>
        <p>
          The <code>xmlsource</code> is a placeholder for your actual XML
          source. You can supply a <code>new StreamSource( new
          StringReader(xmlstring))</code> if you have to read the XML from a
          string. Constructing an XML string and reparse it is not always a good
          iea, consider to use a SAXSource if you generate your XML. You can, of
          course, supply a DOMSource or whatever you like. You can also use
          dynamically generated XSL if you want to.
        </p>
        <p>
          Because you have an explicit transformer object, you can set
          parameters for the transformation run too.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How do I pass parameters to the XSLT transformation?</question>
      <answer>
        <p>
          See the end of the answer for the question above.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How do I use my own fonts when running FOP from a servlet?</question>
      <answer>
        <p>
          Declare the fonts in the <code>userconfig.xml</code> file as
          usual. See <jump href="#usercfg">loading the user configuration
          file</jump> for further steps.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How do I set the baseDir property in a servlet environment?</question>
      <answer>
        <p>
          Use:
        </p>
        <p>
          You need to use the FOUserAgent that contains a base url.
          for caveats.
        </p>
      </answer>
    </faq>
    <faq>
      <question>I keep getting NoClassDefFound and other exceptions. How do I
        get FOP working for various servlet engines?</question>
      <answer>
        <p>
          There are various classpath issues, and possible conflicts with
          existing XML/XSLT libraries. Because servlet containers often use
          their own classloaders for loading webapps, bugs and security problems
          can be bothersome as well.
        </p>
        <p>
          Tomcat comes with detailed instructions for installing FOP and Cocoon,
          check the documentation. There are known bugs to be circumvented, in
          particular in Tomcat 4.0.3.
        </p>
        <p>
          Websphere 3.5: See next question.
        </p>
      </answer>
    </faq>
    <faq>
      <question>FOP in IBM Websphere 3.5</question>
      <answer>
        <p>
          Put a copy of a working parser in some directory where WebSphere can
          access it, for example, if /usr/webapps/yourapp/servlets is the
          classpath for your servlets, copy the Xerces jar into it (any other
          directory would also be fine). Do not add the jar to the servlet
          classpath, but add it to the classpath of the application server which
          contains your web application. In the WebSphere administration
          console, click on the "environment" button in the "general" tab. Fill
          CLASSPATH in the "variable name" box and
          /usr/webapps/yourapp/servlets/Xerces.jar (or whatever your complete
          path is) in the value box, press "OK", then apply the change and
          restart the application server.
        </p>
      </answer>
    </faq>
    <faq>
      <question>FOP and multithreading</question>
      <answer>
        <p>
          FOP is not completely thread safe. At the very least you'll have to
          create a Driver object for every thread unless you prefer your threads
          being blocked.
        </p>
        <p>
          Even though the relevant methods of the Driver object are
          synchronized, there are still problems because FOP uses static
          variables for configuration data and loading images. Be sure not
          to change the configuration data while there is a Driver object
          rendering. It is recommended to setup the configuration only
          once while initialising the servlet. If you have to change the
          configuration data more often, or if you have several servlets
          within the same webapp using FOP, consider implementing a
          singleton class encapsulating both the configuration settings
          and running FOP in synchronized methods.
        </p>
      </answer>
    </faq>
  </part>
  <part>
    <title>Batik/SVG specific questions</title>
    <faq>
      <question>SVG text rendered in bad quality. How do I put SVG text as text
      into PDF?</question>
      <answer>
        <p>
          There is an implementation of a Batik bridge and text painter
          that handles SVG text nodes.
          If it is possible for this to draw the text as PDF text in the
          PDF document then it will do so otherwise the stroking
          text painter is used. There are some cases that are not implemented
          yet such as tspan and outlined text. See
          <link href="svg.html">SVG page</link> for more details.
        </p>
      </answer>
    </faq>
    <faq>
      <question>How do I use FOP with SVG on headless servers?</question>
      <answer>
        <p>
          Batik uses AWT classes for rendering SVG, which in turn needs an X
          server on Unixish systems. If you run a server without X, or if you
          can't connect to the X server due to security restrictions or
          policies, SVG rendering will fail.
        </p>
        <p>
          There are still several options:
        </p>
        <ul>
          <li>
            If you are using JDK 1.4, start it with the -Djava.awt.headless=true
            command line option.
          </li>
          <li>
            Install a X server which provides an im-memory framebuffer without
            actually using a screen device or any display hardware, like Xvfb.
          </li>
          <li>
            Use a toolkit which emulates AWT without the need of an underlying X
            server, like <link
            href="http://www.eteks.com/pja/en">PJA</link>. The PJA toolkit is
            free and comes with detailed installation instructions.
          </li>
        </ul>
      </answer>
    </faq>
    <faq id="svghangs">
      <question>FOP does not exit if a SVG is included.</question>
      <answer>
        <p>
          Applies to older FOP versions and JDK 1.3 and older. That's because
          there is an AWT thread hanging around. The solution is to put a
          System.exit(0) somewhere.
        </p>
      </answer>
    </faq>
    <faq>
      <question>Problems with SVG referring to gradients etc. using
        "uri(#stuff)" (MalformedURLException or stuff not found)</question>
      <answer>
        <p>
          This is really a "resolving relative URI" problem with some
          twists. The problem is that the <code>#stuff</code> URL fragment
          identifier is resolved within the current SVG document. So the
          reference must be valid within the XML subset and it cannot
          reference other SVG documents in the same XML file. Some options
          to try:
        </p>
        <ul>
          <li>
            Put the SVG into a separate file and use it with
            fo:external-graphics.
          </li>
          <li>
            Use a separate SVG file which contains only the gradient (and
            perhaps other SVG stuff you want to reference) and point an absolute
            URL to it:
            <code>fill="url(file:///c:/refstuff/grad.svg#PurpleToWhite)"</code>.
          </li>
          <li>
            Same as above but use a relative URL:
            <code>fill="url(grad.svg#PurpleToWhite)"</code>. This may be easier
            to deploy.
          </li>
          <li>
            Make sure that the reference is valid in the current SVG document.
          </li>
        </ul>
        <p>
          In any case, the referenced stuff has to be pointed to by an URL. It
          doesn't necessarily have to be a file URL, HTTP should also
          work. Also, expect a performance hit in all cases, because another XML
          file has to be retrieved and parsed.
        </p>
        <p>
          Ultimately, both FOP and especially Batik should be fixed to make
          your code work as expected, but this will not only take some time
          but also some effort by a standard committee in order to make the
          semantics of this kind of references in embedded SVG clearer.
        </p>
        <p>See also <link>MalformedURLException</link></p>
      </answer>
    </faq>
  </part>
  <part>
    <title>PDF specific (includes Acrobat peculiarities)</title>
    <faq>
      <question>How do I embed fonts in PDF?</question>
      <answer>
        <p>
          Provide$$$
        </p>
      </answer>
    </faq>
    <faq>
      <question>Characters not displayed, or displayed incorrectly, or displayed
  as "#"</question>
      <answer>
        <p>  Answers are that fonts must be available on the target platform, and
  the selected font must contain glyphs for the desired character.
</p>
        <p>  For example, for most symbols, the symbol font has to be selected
  explicitely (actually: is this a feature or a bug?):
</p>
<p>   &lt;fo:inline font-family="Symbol">&amp;#x2205;&lt;/fo:inline></p>
<p>  gives EMPTY SET while the same characters in the default font results
  in AE LIGATURE (which happens to occupy the same place in the default
  font as the EMPTY SET in the Symbol font). The "#" shows up if the
  selected font does not define a glyph for the translated index.</p>
        <p>(Still applicable in 0.20.3?)</p>
      </answer>
    </faq>
    <faq>
      <question>PDF encryption, PDF protection (read-only)</question>
      <answer>
  <p>use some other tool to postprocess the PDF (itext, or something?)</p>
      </answer>
    </faq>
    <faq>
      <question>Watermarks</question>
      <answer>
        <p>  Answer: see 3.3, or use a a region overlapping the flowing text and put
  an image there: 
</p>
        <p>   > From: Trevor_Campbell@kaz.com.au
    Use the region-before.  Make it large enough to contain your image and then
    include a block (and if required an absolutely positioned block-container)
    with your image in the static-content for the region-before.
  Could use some code here...
        </p>
      </answer>
    </faq>
    <faq>
      <question>PDF prints contorted</question>
      <answer>
        <p>Check paper size in Acrobat settings and "fit to page" (or something)</p>
      </answer>
    </faq>
    <faq>
      <question>Controlling Acrobat bookmark display</question>
      <answer>
        <p>  Not possible with FOP. Postprocess the PDF.</p>
      </answer>
    </faq>
    <faq>
      <question>PDF (more precise: Acrobat Reader) and IEx</question>
      <answer>
        <p>see #later</p>
      </answer>
    </faq>
  </part>
  <part>
    <title>IEx specific stuff</title>
    <faq>
      <question>The FOP servlet is called multiple times.</question>
      <answer>
        <p>
          This is a problem of Internet Explorer requesting the content several
          times. Some suggestions:
        </p>
        <ul>
          <li>
            Use a URL ending in <code>.pdf</code>, like
            <code>http://myserver/servlet/stuff.pdf</code>. Yes, the servlet can
            be configured to handle this. If the URL has to contain parameters,
            try to have both the base URL as well as the last parameter end in
            <code>.pdf</code>, if necessary append a dummy parameter, like
            <code>http://myserver/servlet/stuff.pdf?par1=a&amp;par2=b&amp;d=.pdf</code>. The
            effect may depend on IEx version.
          </li>
          <li>
            Give IEx the opportunity to cache. In particular, ensure the server
            does not set any headers causing IEx not to cache the content. This
            may be a real problem if the document is sent over HTTPS. Consult
            your server manual.
          </li>
          <li>
            Cache in the server. Including a parameter in the URL which has a
            timestamp as the value may help you to decide whether a request is
            repeated. IEx is reported to retrieve a document up to three times,
            but never more often.
          </li>
        </ul>
      </answer>
    </faq>
    <faq>
      <question>How do I print PDF directly from the browser?</question>
      <answer>
        <p>
          It depends whether you mean "printing to a printer under control of the
          server" or "printing on the client's printer".
        </p>
        <p>
          For the first problem, look at the print servlet in the FOP
          examples. You'll have to gather any printer settings in an HTML form
          and send it to the server.
        </p>
        <p>
          For the second task, you can use some client side script to start
          Acrobat Reader in print mode, or use a Java applet based on the FOP
          print servlet. This depends heavily on the client installation and
          should not relied on except in tightly controlled environments.
        </p>
        <p>
          See also http://marc.theaimsgroup.com/?l=fop-dev&amp;m=101065988325115&amp;w=2
        </p>
      </answer>
    </faq>
  </part>
  <part>
    <title>More general questions regarding XSLT and XSLFO and basic XML</title>
    <faq>
      <question>(FO) How do I vertically center an image or a table (or
      whatever)?</question>
      <answer>
        <p>
          Use display-align="center". FOP implements this for block containers
          and table cell. A small self-contained document centering an image on
          a page:
        </p>
        <source><![CDATA[<?xml version="1.0"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format"
  xmlns:svg="http://www.w3.org/2000/svg">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="content"
      page-width="210mm" page-height="297mm">
      <fo:region-body/>
    </fo:simple-page-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="content">
    <fo:flow flow-name="xsl-region-body">
      <fo:table table-layout="fixed" width="100%">
        <fo:table-column column-width="proportional-column-width(1)"/>
        <fo:table-body>
          <fo:table-row height="297mm">
            <fo:table-cell display-align="center">
              <fo:block text-align="center">
                <fo:external-graphic src="fop.jpg"/>
              </fo:block>
            </fo:table-cell>
          </fo:table-row>
        </fo:table-body>
      </fo:table>
    </fo:flow>
  </fo:page-sequence>
</fo:root>]]></source>
      </answer>
    </faq>
    <faq>
      <question>(FO) How to get page numbers printed on the "outer side" of the
        page (for books, obviously)?</question>
      <answer>
        <p>
          That's about different static content on <jump
          href="#oddeven">odd/even pages</jump>.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(FO) How do I get a special header on the first page?</question>
      <answer>
        <p>
          You can insert it into the flow instead of the static content.
          Alternatively, use a page master referring to different page masters
          for the first page and the rest. It is quite similar to the odd/even
          page mechanism. A code sample:
        </p>
        <source><![CDATA[<?xml version="1.0"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="first"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body margin-bottom="20mm"/>
      <fo:region-after region-name="footer-first" extent="20mm"/>
    </fo:simple-page-master>
    <fo:simple-page-master master-name="rest"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body margin-bottom="20mm"/>
      <fo:region-after region-name="footer-rest" extent="20mm"/>
    </fo:simple-page-master>
    <fo:page-sequence-master master-name="document">
      <fo:repeatable-page-master-alternatives>
        <fo:conditional-page-master-reference page-position="first"
          master-reference="first"/>
        <fo:conditional-page-master-reference page-position="rest"
          master-reference="rest"/>
      </fo:repeatable-page-master-alternatives>
    </fo:page-sequence-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="document">
    <fo:static-content flow-name="footer-first">
      <fo:block text-align="center">First page.</fo:block>
    </fo:static-content>
    <fo:static-content flow-name="footer-rest">
      <fo:block text-align-last="center">Other page.</fo:block>
    </fo:static-content>
    <fo:flow flow-name="xsl-region-body">
      <fo:block/>
      <fo:block break-before="page"/>
      <fo:block break-before="page"/>
    </fo:flow>
  </fo:page-sequence>
</fo:root>]]></source>
      </answer>
    </faq>
    <faq id="oddeven">
      <question>(FO) Different static content for odd/even pages</question>
      <answer>
        <p>
          There are examples in the FO distribution and in the XSL FAQ FO
          section http://www.dpawson.co.uk/xsl/sect3/index.html
        </p>
        <p>
          Define a page master with alternating pages masters for odd and even
          pages, specify appropriate regions in these page masters, and be sure
          to give them different names. You use these names to put different
          static content in these regions. A self contained document
          demonstrating this:
        </p>
        <source><![CDATA[<?xml version="1.0"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="even"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body margin-bottom="20mm"/>
      <fo:region-after region-name="footer-even" extent="20mm"/>
    </fo:simple-page-master>
    <fo:simple-page-master master-name="odd"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body margin-bottom="20mm"/>
      <fo:region-after region-name="footer-odd" extent="20mm"/>
    </fo:simple-page-master>
    <fo:page-sequence-master master-name="document">
      <fo:repeatable-page-master-alternatives>
        <fo:conditional-page-master-reference odd-or-even="even"
          master-reference="even"/>
        <fo:conditional-page-master-reference odd-or-even="odd"
          master-reference="odd"/>
      </fo:repeatable-page-master-alternatives>
    </fo:page-sequence-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="document">
    <fo:static-content flow-name="footer-even">
      <fo:block text-align="start"><fo:page-number/></fo:block>
    </fo:static-content>
    <fo:static-content flow-name="footer-odd">
      <fo:block text-align-last="end"><fo:page-number/></fo:block>
    </fo:static-content>
    <fo:flow flow-name="xsl-region-body">
      <fo:block/>
      <fo:block break-before="page"/>
    </fo:flow>
  </fo:page-sequence>
</fo:root>]]></source>
      </answer>
    </faq>
    <faq>
      <question>(FO) How do I omit my headers on a blank page? How do I write
      "This page is left blank" on an intentionally blank page?</question>
      <answer>
        <p>
          A blank page can be forced by a <code>break-before="page-even"</code>
          or similar properties, or by a force-page-count="end-on-odd" on a page
          sequence, which ensures a new chapter or something starts on the
          preferred page.
        </p>
        <p>
          You can define a conditional page master with a page master specific
          for blank pages. This allows you to specify static content for blank
          pages (by definition, a page is blank if no content from a flow is
          rendered on the page). You can omit your normal headers and footers,
          and use for example an extended header to print the "..left blank"
          statement.
        </p>
        <source><![CDATA[<?xml version="1.0"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="normal"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body margin-bottom="20mm"/>
      <fo:region-after region-name="footer-normal" extent="20mm"/>
    </fo:simple-page-master>
    <fo:simple-page-master master-name="blank"
      page-height="297mm" page-width="210mm"
      margin-top="20mm" margin-bottom="20mm"
      margin-left="25mm" margin-right="25mm">
      <fo:region-body/>
      <fo:region-before region-name="header-blank" extent="297mm"/>
    </fo:simple-page-master>
    <fo:page-sequence-master master-name="document">
      <fo:repeatable-page-master-alternatives>
        <fo:conditional-page-master-reference blank-or-not-blank="not-blank"
          master-reference="normal"/>
        <fo:conditional-page-master-reference blank-or-not-blank="blank"
          master-reference="blank"/>
      </fo:repeatable-page-master-alternatives>
    </fo:page-sequence-master>
  </fo:layout-master-set>
  <fo:page-sequence master-reference="document" force-page-count="end-on-even">
    <fo:static-content flow-name="footer-normal">
      <fo:block text-align="center">Normal footer</fo:block>
    </fo:static-content>
    <fo:static-content flow-name="header-blank">
      <fo:block space-before="100mm" text-align-last="center">
        Intentionally left blank.</fo:block>
    </fo:static-content>
    <fo:flow flow-name="xsl-region-body">
      <fo:block/>
    </fo:flow>
  </fo:page-sequence>
</fo:root>]]></source>
      </answer>
    </faq>
    <faq>
      <question>(FO) How to get Euro sign/checkbox/some other stuff</question>
      <answer>
        <p>
          Try to look it up in the Unicode reference at the <link
            href="http://www.unicode.org">Unicode Consortium</link>, in
            particular search the <link
            href="http://www.unicode.org/charts/charindex.html">reference by
            name</link>. Use <link
            href="http://www.w3.org/TR/2000/REC-xml-20001006#sec-references">XML
            character references</link> to put the character into your source
          XML, XSLT or FO.
        </p>
        <p>
          Watch out for font traps, see #, change font temporarily using
          fo:inline if necessary.
        </p>
        <p>
          Alternative: Use an embedded graphic: GIF, PNG, SVG, whatever.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(FO) How do I keep linebreaks/hard spaces? How do I get
        preformatted text displayed as expected.</question>
      <answer>
        <p>
          The specification provides some properties for this: <link
          href="http://www.w3.org/TR/xsl/slice7.html#white-space-collapse">white
          space collapsing</link> and <link
          href="http://www.w3.org/TR/xsl/slice7.html#linefeed-treatment">line
          feed treatment</link>. In FOP, use white-space-collapse="false" on an
          enclosing block. This will also preserve line breaks (which is
          actually a bug, expect this to be changed).
        </p>
      </answer>
    </faq>
    <faq>
      <question>(FO) How do I print the total number of pages, like in "page 1
      of 12"</question>
      <answer>
        <p>
          (XSL FAQ)
        </p>
        <p>
          Put an empty block with an id at the end of the flow:
        </p>
        <source><![CDATA[<fo:flow ...>
   ...
  <fo:block id="last-page"/>
 </fo:flow>]]></source>
        <p>
          Get the number of the last page as follows:
        </p>
        <source><![CDATA[ <fo:page-nuber-citation ref-id="last-page"/>]]></source>
        <p>
          This does not work for all problems, for example if you have multiple
          page sequences, an initial page number different from 1, or if you
          force a certain page count, thereby producing blank pages at the end.
        </p>
        <p>
          There is no reliable way to get the real total page count with FO
          mechanisms, you can only get <em>page numbers</em>.
        </p>
        <p>
          The FOP library provides a method to get the total page count after a
          FO document has been rendered. You can implement your own wrapper to
          do a dummy rendering, inquire the total page count and the perform the
          real rendering, passing the total page count to the XSLT processor to
          splice it into the generated FO. A sample code:
        </p>
        <source><![CDATA[import org.apache.fop.apps.*;
import org.xml.sax.*;
import java.io.*;
import javax.xml.transform.*;
import javax.xml.transform.sax.*;
import javax.xml.transform.stream.*;

class rendtest {

  public static void main(String args[]) {
    try {
      Driver driver=new Driver();
      driver.setOutputStream(new FileOutputStream(args[2]));
      driver.setRenderer(Driver.RENDER_PDF);
      Transformer transformer=TransformerFactory.newInstance()
        .newTransformer(new StreamSource(new File(args[1])));
      transformer.setParameter("page-count","#");
      transformer.transform(new StreamSource(new File(args[0])),
        new SAXResult(driver.getContentHandler()));
      String pageCount=Integer.toString(driver.getResults().getPageCount());
      driver=new Driver();
      driver.setOutputStream(new FileOutputStream(args[2]));
      driver.setRenderer(Driver.RENDER_PDF);
      transformer=TransformerFactory.newInstance()
        .newTransformer(new StreamSource(new File(args[1])));
      transformer.setParameter("page-count",pageCount);
      transformer.transform(new StreamSource(new File(args[0])),
        new SAXResult(driver.getContentHandler()));
    }
    catch( Exception e) {
      e.printStackTrace();
    }
  }
}]]></source>
        <p>
          Declare and use the parameter "page-count" in your XSLT. Be aware you
          may run into convergence problems: replacing the "#" placeholder from
          the first run by the actual page count may change it.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(FO) The header overlaps body content. The body extends into
      footer.</question>
      <answer>
        <p>
          Contrary to popular opinion, the regions on a page may overlap.
          Defining a certain body region does not automatically constrain other
          regions, this has to be done explicitely.
        </p>
        <p>
          If you have a header region with an extent of 20mm, you should define
          a margin for the body region of at least 20mm too, otherwise the
          header content may overwrite some stuff in the body region. This
          applies similarly to the extent of the after region and the bottom
          margin of the body region.
        </p>
        <p>
          The overlap effect can be used creatively for some purposes.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(FO) How do I get lines in the document, as separators, side
      bars or folding marks?</question>
      <answer>
        <p>
          Several possibilities:
        </p>
        <ul>
          <li>
            Use fo:leader (look up the details in the <link
            href="http://www.w3.org/TR/xsl/slice6.html#fo_leader">XSLFO
            specification</link>, or use a book). For horizontal lines only.
          </li>
          <li>
            Use a solid border on a suitable fo:block. Horizontal and vertical
            lines only.
          </li>
          <li>
            Insert a graphic. GIF, PNG SVG, whatever.
          </li>
        </ul>
      </answer>
    </faq>
    <faq>
      <question>(XML) Complaints about &amp;nbsp;. How do I get a non-breaking
      space in FO?</question>
      <answer>
        <p>
          Use &amp;#160; everywhere. In your own XML, you could also use a DTD
          which declares the entity.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(XML) There are complaints about undefined entities, for example
      complaints about &amp;uuml; which used to work in HTML. How do I enter
      special characters like in HTML?</question>
      <answer>
        <p>
          Don't use names as in HTML, use numbers (unless you have a DTD which
          declares the entities). For predefined HTML entities and their Unicode
          codepoints see <link
          href="http://www.w3.org/TR/html4/sgml/entities.html">Character entity
          references in HTML 4</link>
        </p>
      </answer>
    </faq>
    <faq>
      <question>(XML) There are complaints about illegal characters and entities
      in the input.</question>
      <answer>
        <p>
          Make sure ampersands in text and attributes are written as &amp;amp;,
          "&lt;" is written as &amp;lt; and ">" as &amp;gt;. It's not necessary
          everywhere but do it just to be sure.
        </p>
        <p>
          The XML parser should give the proper line and possibly column for
          offending characters.
        </p>
        <p>
          Refer to the <link>XML specification</link> or to a good tutorial for
          details of the XML file format.
        </p>
      </answer>
    </faq>
    <faq>
      <question>(XML) There are complaints about illegal bytes or characters in
      the input. There are odd characters in the result.</question>
      <answer>
        <p>
          Usually, this is a character encoding problem. See <link
          href="http://www.dpawson.co.uk/xsl">XSL FAQ</link>. Many software
          packages producing XML, in particular most XSLT processors, produce by
          default UTF-8 encoded files. If you view them with something not aware
          of the encoding, like Notepad for Win95/98/ME/NT, funny characters are
          displayed. A &Aring; is a giveaway.
        </p>
      </answer>
    </faq>
  </part>
  <part>
    <title>General suggestions. How to solve problems</title>
    <faq>
      <question>Where to post bugs</question>
      <answer>
        <p>
          See docs. See also <jump href="#postquestions">"where to post
          questions"</jump>.
        </p>
      </answer>
    </faq>
    <faq id="postquestions">
      <question>Where to post questions.</question>
      <answer>
        <p>
          Decide where to post:
        </p>
        <ul>
          <li>
            You get exceptions. First, check the FAQ whether the exception is
            mentioned. ClassNotFoundException, NoSuchMethodException and
            NoSuchFieldException problems are almost always a problem with the
            local environment. Check <link
            href="http://nagoya.apache.org">bugzilla</link>. If still not found,
            post to fop-dev.
          </li>
          <li>
            Something doesn't work with FOP but works with another formatter
            (AntennaHouse, PassiveTex). Check whether this is already mentioned
            in the release notes, the FOP limitations document or the FAQ. Post
            to fop-dev or open a bug on <link
            href="http://nagoya.apache.org">bugzilla</link>.
          </li>
          <li>
            Question about how to use FOP, how to perform certain tasks with FOP
            or how to integrate FOP into another application should be posted to
            fop-user.
          </li>
          <li>
            XSLT specific stuff sould go to the <link
            href="http://www.mulberrytech.com/xsl/xsl-list/">XSL
            list</link>. This includes problems with the language and XSLT
            How-Tos.
          </li>
          <li>
            Problems specific to a certain XSLT processor, like Xalan, Saxon or
            MSXML, should be handled by processor specific lists. This includes
            problems with deployment, processor specific extensions, suspected
            bugs and processor specific APIs.
          </li>
          <li>
            Problems with servlet containers should be asked on the vendor
            specific lists for these software packets.
          </li>
          <li>
            More general questions regarding Java, including deployment, Java
            APIs, classpath issues and property definitions should be redirected
            to some Java specific list.
          </li>
        </ul>
      </answer>
    </faq>
  </part>
</faqs>