>>> single line
    code

<<<
<pre><code>code
</code></pre>
>>> include leading whitespace after indentation
    zero
     one
      two
       three

<<<
<pre><code>zero
 one
  two
   three
</code></pre>
>>> code blocks separated by newlines form one block
    zero
    one

    two

    three

<<<
<pre><code>zero
one

two

three
</code></pre>
>>> code blocks separated by two newlines form multiple blocks
    zero
    one


    two


    three

<<<
<pre><code>zero
one


two


three
</code></pre>
>>> escape HTML characters
    <&>

<<<
<pre><code>&lt;&amp;&gt;
</code></pre>
>>> issue #497
    'foo'
<<<
<pre><code>'foo'
</code></pre>