title: How to make datatable headers span a number of columns
body: <p>I have a simple JSF datatable, which currently has four columns, one header row and (with current data) three data rows.</p>
  
  <p>I have to add three extra columns; that part's easy.<br>
  I also want to add another header row before the existing header row with headers that span a subset of the columns.</p>
  
  <p>The desired result is something like:<br>
  Column 1: first row empty; header on second row.<br>
  Columns 2-4: first row header spans 3 columns; second row has individual column headers.<br>
  Columns 5-7: first row header spans 3 columns; second row has individual column headers.  </p>
  
  <p>Is this possible? If so, how do I do it?</p>
  
  <p>Following are images showing what it should look like.</p>
  
  <ol>
  <li><p>This is the data table before I've changed anything.<br>
  <a href="http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample1.gif">Table Example 1 http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample1.gif</a></p></li>
  <li><p>This is the data table after I've added three columns. I was able to do this easily.<br>
  <a href="http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample2.gif">Table Example 1 http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample2.gif</a></p></li>
  <li><p>This shows the desired end result, which I can't figure out. Note the "Retail Sales" and "Fleet/Gov Sales" headers each span three columns.<br>
  <a href="http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample3.gif">Table Example 1 http://www.isw.com.au/home/sjleis/stuff.nsf/tableexample3.gif</a></p></li>
  </ol>