title: jpgraph: display range in line chart
body: <p>Is it possible to display a transparent color for a special range in a line chart?</p>
  
  <p>For example I want to show temperature as a line chart. There are normally values between 22 and 25°C. I want to show a range between 23 and 24°C with a transparent green. Values above or below this range don't have such a transparent background.</p>
  
  <p>I hope you understand what I mean...</p>
  
  <pre><code>$graph = new Graph(900,300);
  $graph-&gt;SetScale("lin");
  
  $p1 = new LinePlot($datay);
  $graph-&gt;Add($p1);
  $p1-&gt;SetColor("#6495ED");
  $p1-&gt;SetLegend('°C');
  
  $sline = new PlotLine(HORIZONTAL,23,'green'); 
  $graph-&gt;Add($sline);
  
  $sline = new PlotLine(HORIZONTAL,24,'green'); 
  $graph-&gt;Add($sline);
  
  $graph-&gt;Stroke();
  </code></pre>