title: If-Then-Else for my simple HTML form
body: <p>I've set up a server, which sends the following form to a client and tries to receive the submitted information. How can I add a If-Else to it as simple as possible? I need to say if the "use tracefile" is enabled, then show the dropdown box, otherwise, show the customized inputs so that user can enter his/her numbers?
  My second concern is that the form does not seem very beautiful. How can I make it aligned, all input boxes be aligned, and such?</p>
  
  <pre><code>    &lt;html&gt;
  &lt;body&gt;
      &lt;p&gt;
      &lt;h3&gt;Please select a configuration below to run the emulator with:&lt;/h3&gt;
      &lt;form action="run.html" method="GET"&gt;
          &lt;input type="checkbox" name="-w" value="-w"&gt;[-w]: wrap around at tracefile end and begin anew at time zero. &lt;/input&gt;
  &lt;br&gt;
  &lt;input type="checkbox" name="-z" value="-w"&gt;[-z]: zero packets routed through; route to co-resident webserver  
  &lt;/input&gt;
  &lt;br&gt;
  &lt;br&gt; YSE Emulator to Run: &lt;select name="yse"&gt;
              &lt;option value="yse1"&gt;YSE1&lt;/option&gt;
              &lt;option value="yse2"&gt;YSE2&lt;/option&gt;
              &lt;option value="yse3"&gt;YSE3&lt;/option&gt;
              &lt;option value="yse4"&gt;YSE4&lt;/option&gt;
              &lt;option value="yse5"&gt;YSE5&lt;/option&gt;
              &lt;option value="yse6"&gt;YSE6&lt;/option&gt;      
          &lt;/select&gt; &lt;br&gt; 
  &lt;br&gt;        
      &lt;input type="checkbox" id="isTracefile" checked/&gt;Use a sample tracefile
      &lt;br&gt;Sample Tracefiles to use: &lt;select name="tracefile"&gt;
              &lt;option value="capacity.1Mbps_c50.txt"&gt;capacity.1Mbps_c50&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.00001.txt"&gt;capacity.3Mbps_100RTT_PER_0.00001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.0001.txt"&gt;capacity.3Mbps_100RTT_PER_0.0001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.001.txt"&gt;capacity.3Mbps_100RTT_PER_0.001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.01.txt"&gt;capacity.3Mbps_100RTT_PER_0.01&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.05.txt"&gt;capacity.3Mbps_100RTT_PER_0.05&lt;/option&gt;
              &lt;option value="capacity.3Mbps_100RTT_PER_0.1.txt"&gt;capacity.3Mbps_100RTT_PER_0.1&lt;/option&gt;
              &lt;option value="capacity.3Mbps_200RTT_PER_0.0001.txt"&gt;capacity.3Mbps_200RTT_PER_0.0001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_200RTT_PER_0.001.txt"&gt;capacity.3Mbps_200RTT_PER_0.001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_400RTT_PER_0.0001.txt"&gt;capacity.3Mbps_400RTT_PER_0.0001&lt;/option&gt;
              &lt;option value="capacity.3Mbps_400RTT_PER_0.001.txt"&gt;capacity.3Mbps_400RTT_PER_0.001&lt;/option&gt;
              &lt;option value="capacity.13Mbps_200RTT_PER_0.000001.txt"&gt;capacity.13Mbps_200RTT_PER_0.000001&lt;/option&gt;
          &lt;/select&gt; 
  &lt;br&gt;
  &lt;b&gt; OR &lt;/b&gt;
  &lt;br&gt;
  &lt;label&gt;Forward Delay: &lt;/label&gt;&lt;input id="fd" type="number" min="0" max="1000" step="1" value ="100"&gt; ms&lt;/input&gt;
  &lt;br&gt;
  &lt;label&gt;Reverse Delay: &lt;/label&gt;&lt;input id="rd" type="number" min="0" max="1000" step="1" value ="100"&gt; ms&lt;/input&gt;
  &lt;br&gt;
  &lt;label&gt;Download Capacity: &lt;/label&gt;&lt;input id="down" type="number" min="1" max="30" step="1" value ="1"&gt; MBps &lt;/input&gt;
  &lt;br&gt;
  &lt;label&gt;Upload Capacity: &lt;/label&gt;&lt;input id="up" type="number" min="1" max="30" step="1" value ="1"&gt; MBps &lt;/input&gt;
  &lt;br&gt;
  &lt;label&gt;Packet Error Rate (PER): &lt;/label&gt;&lt;input id="per" type="number" min="0.00001" max="1" step="0.00001" value ="0.00001"&gt;&lt;/input&gt;
  &lt;br&gt;
  
  &lt;br&gt; &lt;input type="submit" value="Run Emulator!"&gt;
      &lt;/form&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>