+<p>The possible operand encodings are:</p>
+
+<ul>
+<li>1 - Fixed - The field should be emitted as a <a
+ href="#fixedwidth">fixed-width value</a>, whose width
+ is specified by the operand's extra data.</li>
+<li>2 - VBR - The field should be emitted as a <a
+ href="#variablewidth">variable-width value</a>, whose width
+ is specified by the operand's extra data.</li>
+<li>3 - Array - This field is an array of values. The array operand has no
+ extra data, but expects another operand to follow it which indicates the
+ element type of the array. When reading an array in an abbreviated record,
+ the first integer is a vbr6 that indicates the array length, followed by
+ the encoded elements of the array. An array may only occur as the last
+ operand of an abbreviation (except for the one final operand that gives
+ the array's type).</li>
+<li>4 - Char6 - This field should be emitted as a <a href="#char6">char6-encoded
+ value</a>. This operand type takes no extra data.</li>
+</ul>
+
+<p>For example, target triples in LLVM modules are encoded as a record of the
+form <tt>[TRIPLE, 'a', 'b', 'c', 'd']</tt>. Consider if the bitstream emitted
+the following abbrev entry:</p>
+
+<ul>
+<li><tt>[0, Fixed, 4]</tt></li>
+<li><tt>[0, Array]</tt></li>
+<li><tt>[0, Char6]</tt></li>
+</ul>
+
+<p>When emitting a record with this abbreviation, the above entry would be
+emitted as:</p>
+
+<p><tt>[4<sub>abbrevwidth</sub>, 2<sub>4</sub>, 4<sub>vbr6</sub>,
+ 0<sub>6</sub>, 1<sub>6</sub>, 2<sub>6</sub>, 3<sub>6</sub>]</tt></p>
+
+<p>These values are:</p>
+
+<ol>
+<li>The first value, 4, is the abbreviation ID for this abbreviation.</li>
+<li>The second value, 2, is the code for TRIPLE in LLVM IR files.</li>
+<li>The third value, 4, is the length of the array.</li>
+<li>The rest of the values are the char6 encoded values for "abcd".</li>
+</ol>
+
+<p>With this abbreviation, the triple is emitted with only 37 bits (assuming a
+abbrev id width of 3). Without the abbreviation, significantly more space would
+be required to emit the target triple. Also, since the TRIPLE value is not
+emitted as a literal in the abbreviation, the abbreviation can also be used for
+any other string value.
+</p>
+
+</div>
+
+<!-- ======================================================================= -->
+<div class="doc_subsection"><a name="stdblocks">Standard Blocks</a>
+</div>
+
+<div class="doc_text">
+
+<p>
+In addition to the basic block structure and record encodings, the bitstream
+also defines specific builtin block types. These block types specify how the
+stream is to be decoded or other metadata. In the future, new standard blocks
+may be added. Block IDs 0-7 are reserved for standard blocks.
+</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection"><a name="BLOCKINFO">#0 - BLOCKINFO
+Block</a></div>
+
+<div class="doc_text">
+
+<p>The BLOCKINFO block allows the description of metadata for other blocks. The
+ currently specified records are:</p>
+
+<ul>
+<li><tt>[SETBID (#1), blockid]</tt></li>
+<li><tt>[DEFINE_ABBREV, ...]</tt></li>
+</ul>
+
+<p>
+The SETBID record indicates which block ID is being described. SETBID
+records can occur multiple times throughout the block to change which
+block ID is being described. There must be a SETBID record prior to
+any other records.
+</p>
+
+<p>
+Standard DEFINE_ABBREV records can occur inside BLOCKINFO blocks, but unlike
+their occurrence in normal blocks, the abbreviation is defined for blocks
+matching the block ID we are describing, <i>not</i> the BLOCKINFO block itself.
+The abbreviations defined in BLOCKINFO blocks receive abbreviation ids
+as described in <a href="#DEFINE_ABBREV">DEFINE_ABBREV</a>.
+</p>
+
+<p>
+Note that although the data in BLOCKINFO blocks is described as "metadata," the
+abbreviations they contain are essential for parsing records from the
+corresponding blocks. It is not safe to skip them.
+</p>
+
+</div>
+
+<!-- *********************************************************************** -->
+<div class="doc_section"> <a name="wrapper">Bitcode Wrapper Format</a></div>
+<!-- *********************************************************************** -->
+
+<div class="doc_text">
+
+<p>Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper
+structure. This structure contains a simple header that indicates the offset
+and size of the embedded BC file. This allows additional information to be
+stored alongside the BC file. The structure of this file header is:
+</p>
+
+<p>
+<pre>
+[Magic<sub>32</sub>,
+ Version<sub>32</sub>,
+ Offset<sub>32</sub>,
+ Size<sub>32</sub>,
+ CPUType<sub>32</sub>]
+</pre></p>
+
+<p>Each of the fields are 32-bit fields stored in little endian form (as with
+the rest of the bitcode file fields). The Magic number is always
+<tt>0x0B17C0DE</tt> and the version is currently always <tt>0</tt>. The Offset
+field is the offset in bytes to the start of the bitcode stream in the file, and
+the Size field is a size in bytes of the stream. CPUType is a target-specific
+value that can be used to encode the CPU of the target.