title: Search text matching a pattern inside an XML tag
body: <p>I have a file which contains XML tags. Each line has a root element and a couple of sub elements into it. The structure resembles something like this</p>
  
  <pre><code>&lt;document&gt;&lt;title&gt;some title1&lt;/title&gt;&lt;abstract&gt;Some abstract1&lt;/abstract&gt;&lt;/document&gt;
  &lt;document&gt;&lt;title&gt;some title2&lt;/title&gt;&lt;abstract&gt;Some abstract2&lt;/abstract&gt;&lt;/document&gt;
  &lt;document&gt;&lt;title&gt;some title3&lt;/title&gt;&lt;abstract&gt;Some abstract3&lt;/abstract&gt;&lt;/document&gt;
  &lt;document&gt;&lt;title&gt;some title4&lt;/title&gt;&lt;abstract&gt;Some abstract4&lt;/abstract&gt;&lt;/document&gt;
  </code></pre>
  
  <p>Now I have to find all lines where the  tag contains a particular word. eg: get all lines that contain abstract1 inside the <code>&lt;abstract&gt;</code> tag.</p>
  
  <p>How to do it in either grep, awk or sed?</p>