title: Why markdown ignores single line break?
body: <p>I know the solution to make single line break. I just want to know the reason.</p>
  <p>when I input this,</p>
  <pre class="lang-markdown prettyprint-override"><code>line1
  line2
  </code></pre>
  <p>preview of this md file is</p>
  <pre><code>line1line2
  </code></pre>
  <p>Why? is single line break looking bad or what?</p>