title: PHPExcel how to set collapse and expands for groups of row?
body: <p>Suppose I want to set collapse and expand for row 2 up to 4 as one group, and 8 up to 12 the second group. It means when user want to click on expand <code>+</code> icon of group 1, rows from 2 up to 4 should be visible, and for group 2 row from 8 up to 12 should be visible. Bellow is the code for single row.</p>
  
  <pre><code>$sheet-&gt;getRowDimension(1)-&gt;setOutlineLevel(1);
  
  $sheet-&gt;getRowDimension(1)-&gt;setVisible(false);
  
  $sheet-&gt;getRowDimension(1)-&gt;setCollapsed(true);
  </code></pre>
  
  <p>And the other question is, can we define the expand icon ourself instead of <code>+</code> icon?
  some thing like <a href="https://i.stack.imgur.com/ObU08.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/ObU08.jpg" alt="this"></a></p>