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<document>
  <header>
    <title>Apache POI™ - HPSF Internals</title>
    <authors>
      <person name="Rainer Klute" email="klute@rainer-klute.de"/>
    </authors>
  </header>
  <body>
    <section><title>HPSF Internals</title>

    <section><title>Introduction</title>

    <p>A Microsoft Office document is internally organized like a filesystem
     with directory and files. Microsoft calls these files
     <strong>streams</strong>. A document can have properties attached to it,
     like author, title, number of words etc. These metadata are not stored in
     the main stream of, say, a Word document, but instead in a dedicated
     stream with a special format. Usually this stream's name is
     <code>\005SummaryInformation</code>, where <code>\005</code> represents
     the character with a decimal value of 5.</p>

    <p>A single piece of information in the stream is called a
     <strong>property</strong>, for example the document title. Each property
     has an integral <strong>ID</strong> (e.g. 2 for title), a
     <strong>type</strong> (telling that the title is a string of bytes) and a
     <strong>value</strong> (what this is should be obvious). A stream
     containing properties is called a
     <strong>property set stream</strong>.</p>

    <p>This document describes the internal structure of a property set stream,
     i.e. the <strong>HPSF</strong>. It does
     not describe how a Microsoft Office document is organized internally and
     how to retrieve a stream from it. See the <a
      href="../poifs/index.html">POIFS documentation</a> for that kind of
     stuff.</p>

    <p>The HPSF is not only used in the Summary
     Information stream in the top-level document of a Microsoft Office
     document. Often there is also a property set stream named
     <code>\005DocumentSummaryInformation</code> with additional properties.
     Embedded documents may have their own property set streams. You cannot
     tell by a stream's name whether it is a property set stream or not.
     Instead you have to open the stream and look at its bytes.</p>
   </section>



    <section><title>Data Types</title>

    <p>Before delving into the details of the property set stream format we
     have to have a short look at data types. Integral values are stored in the
     so-called <strong>little endian</strong> format. In this format the bytes
     that make out an integral value are stored in the "wrong" order. For
     example, the decimal value 4660 is 0x1234 in the hexadecimal notation. If
     you think this should be represented by a byte 0x12 followed by another
     byte 0x34, you are right. This is called the <strong>big endian</strong>
     format. In the little endian format, however, this order is reversed and
     the low-value byte comes first: 0x3412.
    </p>

    <p>The following table gives an overview about some important data
     types:</p>

    <table>

     <tr>
      <th>Name</th>
      <th>Length</th>
      <th>Example (Big Endian)</th>
      <th>Example (Little Endian)</th>
     </tr>

     <tr>
      <td><strong>Bytes</strong></td>
      <td>1 byte</td>
      <td><code>0x12</code></td>
      <td><code>0x12</code></td>
     </tr>

     <tr>
      <td><strong>Word</strong></td>
      <td>2 bytes</td>
      <td><code>0x1234</code></td>
      <td><code>0x3412</code></td>
     </tr>

     <tr>
      <td><strong>DWord</strong></td>
      <td>4 bytes</td>
      <td><code>0x12345678</code></td>
      <td><code>0x78563412</code></td>
     </tr>

     <tr>
      <td><strong>ClassID</strong><br/>
       A sequence of one DWord, two Words and eight Bytes</td>

      <td>16 bytes</td>

      <td><code>0xE0859FF2F94F6810AB9108002B27B3D9</code> resp.
	<code>E0859FF2-F94F-6810-AB-91-08-00-2B-27-B3-D9</code></td>

      <td><code>0xF29F85E04FF91068AB9108002B27B3D9</code> resp.
	<code>F29F85E0-4FF9-1068-AB-91-08-00-2B-27-B3-D9</code></td>
     </tr>

     <tr>
      <td></td>
      <td></td>
      <td>The ClassID examples are given here in two different notations. The
	second notation without the "0x" at the beginning and with dashes
	inside shows the internal grouping into one DWord, two Words and eight
	Bytes.</td>
      <td><em>Watch out:</em> Microsoft documentation and tools show class IDs
	a little bit differently like
	<code>F29F85E0-4FF9-1068-AB91-08002B27B3D9</code>.
	However, that representation is (intentionally?) misleading with
	respect to endianess.</td>
     </tr>
    </table>
   </section>



   <section><title>HPSF Overview</title>

    <p>A property set stream consists of three main parts:</p>

    <ol>
     <li>The <strong>header</strong> and</li>
     <li>the <strong>section(s)</strong> containing the properties.</li>
    </ol>
   </section>



   <section><title>The Header</title>

    <p>The first bytes in a property set stream is the <strong>header</strong>.
     It has a fixed length and looks like this:</p>

    <table>
      <tr>
       <th>Offset</th>
       <th>Type</th>
       <th>Contents</th>
       <th>Remarks</th>
      </tr>

      <tr>
       <td>0</td>
       <td>Word</td>
       <td><code>0xFFFE</code></td>
       <td>If the first four bytes of a stream do not contain these values, the
	 stream is not a property set stream.</td>
      </tr>

      <tr>
       <td>2</td>
       <td>Word</td>
       <td><code>0x0000</code></td>
      <td></td>
      </tr>

      <tr>
       <td>4</td>
       <td>DWord</td>
       <td>Denotes the operating system and the OS version under which this
	 stream was created. The operating system ID is in the DWord's higher
	 word (after little endian decoding): <code>0x0000</code> for Win16,
	 <code>0x0001</code> for Macintosh and <code>0x0002</code> for Win32 -
         that's all. The reader is most likely aware of the fact that there are
         some more operating systems. However, Microsoft does not seem to
       know.</td>
      <td></td>
      </tr>

      <tr>
       <td>8</td>
       <td>ClassID</td>
       <td><code>0x00000000000000000000000000000000</code></td>
       <td>Most property set streams have this value but this is not
	 required.</td>
      </tr>

      <tr>
       <td>24</td>
       <td>DWord</td>
       <td><code>0x01000000</code> or greater</td>
       <td>Section count. This field's value should be equal to 1 or greater.
	 Microsoft claims that this is a "reserved" field, but it seems to tell
	 how many sections (see below) are following in the stream. This would
	 really make sense because otherwise you could not know where and how
	 far you should read section data.</td>
     </tr>
    </table>
   </section>



   <section><title>Section List</title>

    <p>Following the header is the section list. This is an array of pairs each
     consisting of a section format ID and an offset. This array has as many
     pairs of ClassID and and DWord fields as the section count field in the
     header says. The Summary Information stream contains a single section, the
     Document Summary Information stream contains two.</p>

    <table>
      <tr>
       <th>Type</th>
       <th>Contents</th>
       <th>Remarks</th>
      </tr>

      <tr>
       <td>ClassID</td>
       <td>Section format ID</td>
       <td><code>0xF29F85E04FF91068AB9108002B27B3D9</code> for the single section
	 in the Summary Information stream.<br/><br/>

	<code>0xD5CDD5022E9C101B939708002B2CF9AE</code> for the first
	 section in the Document Summary Information stream.</td>
      </tr>

      <tr>
       <td>DWord</td>
       <td>Offset</td>
       <td>The number of bytes between the beginning of the stream and the
	 beginning of the section within the stream.</td>
      </tr>

      <tr>
       <td>ClassID</td>
       <td>Section format ID</td>
       <td>...</td>
      </tr>

      <tr>
       <td>DWord</td>
       <td>Offset</td>
       <td>...</td>
      </tr>

      <tr>
       <td>...</td>
       <td>...</td>
       <td>...</td>
      </tr>
    </table>
   </section>



   <section><title>Section</title>

    <p>A section is divided into three parts: the section header (with the
     section length and the number of properties in the section), the
     properties list (with type and offset of each property), and the
     properties themselves. Here are the details:</p>

    <table>
      <tr>
       <th>&nbsp;</th>
       <th>Type</th>
       <th>Contents</th>
       <th>Remarks</th>
      </tr>

      <tr>
       <td>Section header</td>

       <td>DWord</td>
       <td>Length</td>
       <td>The length of the section in bytes.</td>
      </tr>

     <tr>
      <td></td>
      <td>DWord</td>
       <td>Property count</td>
       <td>The number of properties in the section.</td>
      </tr>

      <tr>

       <td>Properties list</td>

       <td>DWord</td>
       <td>Property ID</td>
       <td>The property ID tells what the property means. For example, an ID of
	 <code>0x0002</code> in the Summary Information stands for the document's
	title. See the <a href="#property_ids">Property IDs</a>
	 chapter below for more details.</td>
      </tr>

      <tr>
      <td></td>
       <td>DWord</td>
       <td>Offset</td>
       <td>The number of bytes between the beginning of the section and the
	 property.</td>
      </tr>

      <tr>
      <td></td>
       <td>...</td>
       <td>...</td>
       <td>...</td>
      </tr>

      <tr>
       <td>Properties</td>

       <td>DWord</td>
       <td>Property type ("variant")</td>
       <td>This is the property's data type, e.g. an integer value, a byte
	 string or a Unicode string. See the
	 <a href="#property_types"><em>Property Types</em></a> chapter
         for details!</td>
      </tr>

      <tr>
      <td></td>
       <td><em>Field length depends on the property type
	  ("variant")</em></td>
       <td>Property value</td>
       <td>This field's length depends on the property's type. These are the
	 bytes that make out the DWord, the byte string or some other data of
	 fixed or variable length.<br/><br/>

	    The  property value's length is always stored in an area which is a
	 multiple of 4 in length. If the property is shorter, e.g. a byte
	 string of 13 bytes, the remaining bytes are padded with <code>0x00</code>
	 bytes.</td>
      </tr>

      <tr>
      <td></td>
       <td>...</td>
       <td>...</td>
       <td>...</td>
      </tr>
    </table>
   </section>



   <section><title>Property IDs</title>
    <anchor id="property_ids"/>

    <p>As seen above, a section holds a property list: an array with property
     IDs and offsets. The property ID gives each property a meaning. For
     example, in the Summary Information stream the property ID 2 says that
     this property is the document's title.</p>

    <p>If you want to know a property ID's meaning, it is not sufficient to
     know the ID itself. You must also know the
     <strong>section format ID</strong>.  For example, in the Document Summary
     Information stream the property ID 2 means not the document's title but
     its category. Due to Microsoft's infinite wisdom the section format ID is
     not part of the section. Thus if you have only a section without the
     stream it is in, you cannot make any sense of the properties because you
     do not know what they mean.</p>

    <p>So each section format ID has its own name space of property IDs.
     Microsoft defined some "well-known" property IDs for the Summary
     Information and the Document Summary Information streams. You can extend
     them by your own additional IDs. This will be described below.</p>

    <section><title>Property IDs in The Summary Information Stream</title>

     <p>The Summary Information stream has a single section with a section
      format ID of <code>0xF29F85E04FF91068AB9108002B27B3D9</code>. The following
      table defines the meaning of its property IDs. Each row associates a
      property ID with a <em>name</em> and an <em>ID string</em>. (The property
      <em>type</em> is just for informational purposes given here. As we have
      seen above, the type is always given along with the value.)</p>

     <p>The property <em>name</em> is a readable string which could be
      displayed to the user. However, this string is useful only for users who
      understand English. The property name does not help with other
      languages.</p>

     <p>The property <em>ID string</em> is about the same but looks more
      technically and is nothing a user should bother with. You could the ID
      string and map it to an appropriate display string in a particular
      language.  Of course you could do that with the property ID as well and
      with less overhead, but people (including software developers) tend to be
      better in remembering symbolic constants than remembering numbers.</p>

     <table>
      <tr>
       <th>Property ID</th>
       <th>Property Name</th>
       <th>Property ID String</th>
       <th>Property Type</th>
      </tr>
      <tr>
       <td>2</td>
       <td>Title</td>
       <td>PID_TITLE</td>
       <td>VT_LPSTR</td>
      </tr>
       <tr>
	<td>3</td>
	<td>Subject</td>
	<td>PID_SUBJECT</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>4</td>
	<td>Author</td>
	<td>PID_AUTHOR</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>5</td>
	<td>Keywords</td>
	<td>PID_KEYWORDS</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>6</td>
	<td>Comments</td>
	<td>PID_COMMENTS</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>7</td>
	<td>Template</td>
	<td>PID_TEMPLATE</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>8</td>
	<td>Last Saved By</td>
	<td>PID_LASTAUTHOR</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>9</td>
	<td>Revision Number</td>
	<td>PID_REVNUMBER</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>10</td>
	<td>Total Editing Time</td>
	<td>PID_EDITTIME</td>
	<td>VT_FILETIME</td>
       </tr>
       <tr>
	<td>11</td>
	<td>Last Printed</td>
	<td>PID_LASTPRINTED</td>
	<td>VT_FILETIME</td>
       </tr>
       <tr>
	<td>12</td>
	<td>Create Time/Date</td>
	<td>PID_CREATE_DTM</td>
	<td>VT_FILETIME</td>
       </tr>
       <tr>
	<td>13</td>
	<td>Last Saved Time/Date</td>
	<td>PID_LASTSAVE_DTM</td>
	<td>VT_FILETIME</td>
       </tr>
       <tr>
	<td>14</td>
	<td>Number of Pages</td>
	<td>PID_PAGECOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>15</td>
	<td>Number of Words</td>
	<td>PID_WORDCOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>16</td>
	<td>Number of Characters</td>
	<td>PID_CHARCOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>17</td>
	<td>Thumbnail</td>
	<td>PID_THUMBNAIL</td>
	<td>VT_CF</td>
       </tr>
       <tr>
	<td>18</td>
	<td>Name of Creating Application</td>
	<td>PID_APPNAME</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>19</td>
	<td>Security</td>
	<td>PID_SECURITY</td>
	<td>VT_I4</td>
      </tr>
     </table>
    </section>



    <section><title>Property IDs in The Document Summary Information Stream</title>

     <p>The Document Summary Information stream has two sections with a section
      format ID of <code>0xD5CDD5022E9C101B939708002B2CF9AE</code> for the first
      one.  The following table defines the meaning of the property IDs in the
      first section. See the preceding section for interpreting the table.</p>

     <table>
       <tr>
	<th>Property ID</th>
	<th>Property name</th>
	<th>Property ID string</th>
	<th>VT type</th>
       </tr>

       <tr>
	<td>0</td>
	<td>Dictionary</td>
	<td>PID_DICTIONARY</td>
	<td>[Special format]</td>
       </tr>
       <tr>
	<td>1</td>
	<td>Code page</td>
	<td>PID_CODEPAGE</td>
	<td>VT_I2</td>
       </tr>
       <tr>
	<td>2</td>
	<td>Category</td>
	<td>PID_CATEGORY</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>3</td>
	<td>PresentationTarget</td>
	<td>PID_PRESFORMAT</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>4</td>
	<td>Bytes</td>
	<td>PID_BYTECOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>5</td>
	<td>Lines</td>
	<td>PID_LINECOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>6</td>
	<td>Paragraphs</td>
	<td>PID_PARCOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>7</td>
	<td>Slides</td>
	<td>PID_SLIDECOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>8</td>
	<td>Notes</td>
	<td>PID_NOTECOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>9</td>
	<td>HiddenSlides</td>
	<td>PID_HIDDENCOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>10</td>
	<td>MMClips</td>
	<td>PID_MMCLIPCOUNT</td>
	<td>VT_I4</td>
       </tr>
       <tr>
	<td>11</td>
	<td>ScaleCrop</td>
	<td>PID_SCALE</td>
	<td>VT_BOOL</td>
       </tr>
       <tr>
	<td>12</td>
	<td>HeadingPairs</td>
	<td>PID_HEADINGPAIR</td>
	<td>VT_VARIANT | VT_VECTOR</td>
       </tr>
       <tr>
	<td>13</td>
	<td>TitlesofParts</td>
	<td>PID_DOCPARTS</td>
	<td>VT_LPSTR | VT_VECTOR</td>
       </tr>
       <tr>
	<td>14</td>
	<td>Manager</td>
	<td>PID_MANAGER</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>15</td>
	<td>Company</td>
	<td>PID_COMPANY</td>
	<td>VT_LPSTR</td>
       </tr>
       <tr>
	<td>16</td>
	<td>LinksUpTo Date</td>
	<td>PID_LINKSDIRTY</td>
	<td>VT_BOOL</td>
       </tr>
     </table>
    </section>
   </section>



   <section><title>Property Types</title>
    <anchor id="property_types"/>

    <p>A property consists of a DWord <em>type field</em> followed by the
     property value. The property type is an integer value and tells how the
     data byte following it are to be interpreted. In the Microsoft world it is
     also known as the <em>variant</em>.</p>

    <p>The <em>Usage</em> column says where a variant type may occur. Not all
     of them are allowed in a property set but just those marked with a [P].
     <strong>[V]</strong> - may appear in a VARIANT, <strong>[T]</strong> - may
     appear in a TYPEDESC, <strong>[P]</strong> - may appear in an OLE property
     set, <strong>[S]</strong> - may appear in a Safe Array.</p>

    <table>
      <tr>
       <th>Variant ID</th>
       <th>Variant Type</th>
       <th>Usage</th>
       <th>Description</th>
      </tr>
      <tr>
       <td>0</td>
       <td>VT_EMPTY</td>
       <td>[V] [P]</td>
       <td>nothing</td>
      </tr>
      <tr>
       <td>1</td>
       <td>VT_NULL</td>
       <td>[V] [P]</td>
       <td>SQL style Null</td>
      </tr>
      <tr>
       <td>2</td>
       <td>VT_I2</td>
       <td>[V] [T] [P] [S]</td>
       <td>2 byte signed int</td>
      </tr>
      <tr>
       <td>3</td>
       <td>VT_I4</td>
       <td>[V] [T] [P] [S]</td>
       <td>4 byte signed int</td>
      </tr>
      <tr>
       <td>4</td>
       <td>VT_R4</td>
       <td>[V] [T] [P] [S]</td>
       <td>4 byte real</td>
      </tr>
      <tr>
       <td>5</td>
       <td>VT_R8</td>
       <td>[V] [T] [P] [S]</td>
       <td>8 byte real</td>
      </tr>
      <tr>
       <td>6</td>
       <td>VT_CY</td>
       <td>[V] [T] [P] [S]</td>
       <td>currency</td>
      </tr>
      <tr>
       <td>7</td>
       <td>VT_DATE</td>
       <td>[V] [T] [P] [S]</td>
       <td>date</td>
      </tr>
      <tr>
       <td>8</td>
       <td>VT_BSTR</td>
       <td>[V] [T] [P] [S]</td>
       <td>OLE Automation string</td>
      </tr>
      <tr>
       <td>9</td>
       <td>VT_DISPATCH</td>
       <td>[V] [T] [P] [S]</td>
       <td>IDispatch *</td>
      </tr>
      <tr>
       <td>10</td>
       <td>VT_ERROR</td>
       <td>[V] [T] [S]</td>
       <td>SCODE</td>
      </tr>
      <tr>
       <td>11</td>
       <td>VT_BOOL</td>
       <td>[V] [T] [P] [S]</td>
       <td>True=-1, False=0</td>
      </tr>
      <tr>
       <td>12</td>
       <td>VT_VARIANT</td>
       <td>[V] [T] [P] [S]</td>
       <td>VARIANT *</td>
      </tr>
      <tr>
       <td>13</td>
       <td>VT_UNKNOWN</td>
       <td>[V] [T] [S]</td>
       <td>IUnknown *</td>
      </tr>
      <tr>
       <td>14</td>
       <td>VT_DECIMAL</td>
       <td>[V] [T] [S]</td>
       <td>16 byte fixed point</td>
      </tr>
      <tr>
       <td>16</td>
       <td>VT_I1</td>
       <td>[T]</td>
       <td>signed char</td>
      </tr>
      <tr>
       <td>17</td>
       <td>VT_UI1</td>
       <td>[V] [T] [P] [S]</td>
       <td>unsigned char</td>
      </tr>
      <tr>
       <td>18</td>
       <td>VT_UI2</td>
       <td>[T] [P]</td>
       <td>unsigned short</td>
      </tr>
      <tr>
       <td>19</td>
       <td>VT_UI4</td>
       <td>[T] [P]</td>
       <td>unsigned short</td>
      </tr>
      <tr>
       <td>20</td>
       <td>VT_I8</td>
       <td>[T] [P]</td>
       <td>signed 64-bit int</td>
      </tr>
      <tr>
       <td>21</td>
       <td>VT_UI8</td>
       <td>[T] [P]</td>
       <td>unsigned 64-bit int</td>
      </tr>
      <tr>
       <td>22</td>
       <td>VT_INT</td>
       <td>[T]</td>
       <td>signed machine int</td>
      </tr>
      <tr>
       <td>23</td>
       <td>VT_UINT</td>
       <td>[T]</td>
       <td>unsigned machine int</td>
      </tr>
      <tr>
       <td>24</td>
       <td>VT_VOID</td>
       <td>[T]</td>
       <td>C style void</td>
      </tr>
      <tr>
       <td>25</td>
       <td>VT_HRESULT</td>
       <td>[T]</td>
       <td>Standard return type</td>
      </tr>
      <tr>
       <td>26</td>
       <td>VT_PTR</td>
       <td>[T]</td>
       <td>pointer type</td>
      </tr>
      <tr>
       <td>27</td>
       <td>VT_SAFEARRAY</td>
       <td>[T]</td>
       <td>(use VT_ARRAY in VARIANT)</td>
      </tr>
      <tr>
       <td>28</td>
       <td>VT_CARRAY</td>
       <td>[T]</td>
       <td>C style array</td>
      </tr>
      <tr>
       <td>29</td>
       <td>VT_USERDEFINED</td>
       <td>[T]</td>
       <td>user defined type</td>
      </tr>
      <tr>
       <td>30</td>
       <td>VT_LPSTR</td>
       <td>[T] [P]</td>
       <td>null terminated string</td>
      </tr>
      <tr>
       <td>31</td>
       <td>VT_LPWSTR</td>
       <td>[T] [P]</td>
       <td>wide null terminated string</td>
      </tr>
      <tr>
       <td>64</td>
       <td>VT_FILETIME</td>
       <td>[P]</td>
       <td>FILETIME</td>
      </tr>
      <tr>
       <td>65</td>
       <td>VT_BLOB</td>
       <td>[P]</td>
       <td>Length prefixed bytes</td>
      </tr>
      <tr>
       <td>66</td>
       <td>VT_STREAM</td>
       <td>[P]</td>
       <td>Name of the stream follows</td>
      </tr>
      <tr>
       <td>67</td>
       <td>VT_STORAGE</td>
       <td>[P]</td>
       <td>Name of the storage follows</td>
      </tr>
      <tr>
       <td>68</td>
       <td>VT_STREAMED_OBJECT</td>
       <td>[P]</td>
       <td>Stream contains an object</td>
      </tr>
      <tr>
       <td>69</td>
       <td>VT_STORED_OBJECT</td>
       <td>[P]</td>
       <td>Storage contains an object</td>
      </tr>
      <tr>
       <td>70</td>
       <td>VT_BLOB_OBJECT</td>
       <td>[P]</td>
       <td>Blob contains an object</td>
      </tr>
      <tr>
       <td>71</td>
       <td>VT_CF</td>
       <td>[P]</td>
       <td>Clipboard format</td>
      </tr>
      <tr>
       <td>72</td>
       <td>VT_CLSID</td>
       <td>[P]</td>
       <td>A Class ID</td>
      </tr>
      <tr>
       <td>0x1000</td>
       <td>VT_VECTOR</td>
       <td>[P]</td>
       <td>simple counted array</td>
      </tr>
      <tr>
       <td>0x2000</td>
       <td>VT_ARRAY</td>
       <td>[V]</td>
       <td>SAFEARRAY*</td>
      </tr>
      <tr>
       <td>0x4000</td>
       <td>VT_BYREF</td>
       <td>[V]</td>
       <td>void* for local use</td>
      </tr>
      <tr>
       <td>0x8000</td>
       <td>VT_RESERVED</td>
       <td><br/></td>
       <td><br/></td>
      </tr>
      <tr>
       <td>0xFFFF</td>
       <td>VT_ILLEGAL</td>
       <td><br/></td>
       <td><br/></td>
      </tr>
      <tr>
       <td>0xFFF</td>
       <td>VT_ILLEGALMASKED</td>
       <td><br/></td>
       <td><br/></td>
      </tr>
      <tr>
       <td>0xFFF</td>
       <td>VT_TYPEMASK</td>
       <td><br/></td>
       <td><br/></td>
      </tr>
    </table>
   </section>



   <section>
    <title>The Dictionary</title>

    <p>What a dictionary is good for is explained in the <a
      href="how-to.html">HPSF HOW-TO</a>. This chapter explains how it is
     organized internally.</p>

    <p>The dictionary has a simple header consisting of a single UInt value. It
    tells how many entries the dictionary comprises:</p>

    <table>
     <tr>
      <th>Name</th>
      <th>Data type</th>
      <th>Description</th>
     </tr>
     <tr>
      <td>nrEntries</td>
      <th>UInt</th>
      <td>Number of dictionary entries</td>
     </tr>
    </table>

    <p>The dictionary entries follow the header. Each one looks like this:</p>

    <table>
     <tr>
      <th>Name</th>
      <td>Data type</td>
      <th>Description</th>
     </tr>
     <tr>
      <td>key</td>
      <td>UInt</td>
      <td>The unique number of this property, i.e. the PID</td>
     </tr>
     <tr>
      <td>length</td>
      <td>UInt</td>
      <td>The length of the property name associated with the key</td>
     </tr>
     <tr>
      <td>value</td>
      <td>String</td>
      <td>The property's name, terminated with a 0x00 character</td>
     </tr>
    </table>

    <p>The entries are not aligned, i.e. each one follows its predecessor
     without any gap or fill characters.</p>
   </section>



   <section><title>References</title>

    <p>In order to assemble the HPSF description I used information publically
     available on the Internet only. The references given below have been very
     helpful. If you have any amendments or corrections, please let us know!
     Thank you!</p>

    <ol>

     <li>In
      <a href="https://www.kyler.com/pubs/ddj9894.html"><em>Understanding OLE
	documents</em></a>, Ken Kyler gives an introduction to OLE2
      documents and especially to property sets. He names the property names,
      types, and IDs of the Summary Information and Document Summary
      Information stream.</li>

     <li>The <a href="https://www.dwam.net/docs/oleref/"><em>ActiveX
	Programmer's Reference</em></a> at <a
       href="https://www.dwam.net/docs/oleref/">https://www.dwam.net/docs/oleref/</a>
      seems a little outdated, but that's what I have found.</li>

     <li>An overview of the <code>VT_</code> types is in
      <a href="https://www.marin.clara.net/COM/variant_type_definitions.htm"><em>Variant
	Type Definitions</em></a>.</li>

     <li>What is a <code>FILETIME</code>? The answer can be found
      under <a
       href="https://msdn.microsoft.com/library/default.asp?url=/library/en-us/sysinfo/base/filetime_str.asp"></a>, <a href="https://www.vbapi.com/ref/f/filetime.html">https://www.vbapi.com/ref/f/filetime.html</a> or
      <a href="https://www.cs.rpi.edu/courses/fall01/os/FILETIME.html">https://www.cs.rpi.edu/courses/fall01/os/FILETIME.html</a>.
      In short: <em>The FILETIME structure holds a date and time associated
       with a file. The structure identifies a 64-bit integer specifying the
       number of 100-nanosecond intervals which have passed since January 1,
       1601. This 64-bit value is split into the two dwords stored in the
       structure.</em></li>

     <li>Microsoft provides some public information in the <a
       href="https://msdn.microsoft.com/library/default.asp">MSDN
       Library</a>. Use the search function to try to find what you are
      looking for, e.g. "codepage" or "document summary information" etc.</li>
    </ol>
   </section>
  </section>
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</document>

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