hide column (or field) based on dropdown selection

Here are two helpful articles:

http://www.asprunner.com/forums/topic/6504-how-to-disableenable-controls-on-editadd-pages/

http://xlinesoft.com/phprunner/docs/javascript_api.htm

Thanks Jane, this was really helpful.
For other users two ways to do this:

1. Hide the entire row
   
2. Hide the field
   Here's a snippet for others:
   on HTML editor view:
   
   On the row you want to hide
   
   Example: {BEGIN acode_fieldblock}<TRid=acoderow>
   Javascript snippet:
   // dropdown control
   
   var ctrlMrchntid = Runner.getControl(pageid, 'mrchntid');
   
   // target field to appear/disappear
   
   var ctrlAcode = Runner.getControl(pageid, 'acode');
   
   //target row to appear / disappear
   
   var acoderow = document.getElementById("acoderow");
   ctrlMrchntid.on('change', function(e){
   
   if (this.getValue() == 'TESTVAL')
   
   {
   
   // choose whether you want field or entire row
   
   //ctrlAcode.show();
   
   acoderow.style.display = '';
   
   }else{
   
   // choose whether you want field or entire row
   
   //ctrlAcode.hide();
   
   acoderow.style.display = 'none'; }
   }
   
   );