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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V2.0//EN" "document-v20.dtd">

<document>
    <header>
        <title>Hacking HSSF</title>
        <authors>
            <person email="user@poi.apache.org" name="Glen Stampoultzis" id="GJS"/>
            <person email="acoliver@apache.org" name="Andrew Oliver" id="AO"/>
        </authors>
    </header>
    <body>
        <section><title>Where Can I Find Documentation on Feature X</title>
            <p>
                You might find the
                'Excel 97 Developer's Kit' (out of print, Microsoft Press, no
                restrictive covenants, available on Amazon.com) helpful for
                understanding the file format.
            </p>
            <p>
                Also useful is the <a href="https://sc.openoffice.org/excelfileformat.pdf">open office XLS spec</a>.  We
                are collaborating with the maintainer of the spec so if you think you can add something to their
                document just send through your changes.
            </p>
        </section>
        <section><title>Help, I Can't Find Feature X Documented Anywhere</title>
            <ol>
                <li>
                Look at OpenOffice.org or Gnumeric sources if its implemented there.
                </li>
                <li>
                Use org.apache.poi.hssf.dev.BiffViewer to view the structure of the
                file.  Experiment by adding one criteria entry at a time.  See what it
                does to the structure, infer behavior and structure from it.  Using the
                unix diff command (or get cygwin from www.cygwin.com for windows) you
                can figure out a lot very quickly. Unimplemented records show up as
                'UNKNOWN' and prints a hex dump.
                </li>
            </ol>
        </section>
        <section><title>Low-level Record Generation</title>
            <p>
                Low level records can be time consuming to created.  We created a record
                generator to help generate some of the simpler tasks.
            </p>
            <p>
                We use XML
                descriptors to generate the Java code (which sure beats the heck out of
                the PERL scripts originally used ;-) for low level records.  The
                generator is kinda alpha-ish right now and could use some enhancement,
                so you may find that to be about 1/2 of the work.  Notice this is in
                org.apache.poi.hssf.record.definitions.
            </p>
        </section>
        <section><title>Important Notice</title>
            <p>One thing to note:  If you are making a large code contribution we need to ensure
            any participants in this process have never
            signed a "Non Disclosure Agreement" with Microsoft, and have not
            received any information covered by such an agreement.  If they have
            they'll not be able to participate in the POI project.  For large contributions we
            may ask you to sign an agreement.</p>
        </section>
        <section><title>What Can I Work On?</title>
            <p>Ask in the dev mailing list for advice.</p>
        </section>
        <section><title>What Else Should I Know?</title>
            <p>Make sure you <a href="site:guidelines">read the contributing section</a>
            as it contains more generation information about contributing to POI in general.</p>
        </section>
    </body>
</document>
