public interface StringMethods
StringMethod can be specified as a
 String containing a valid
  JavaScript expression.  This expression will automatically be converted to a function
  with a return value matching the value of the last statement.  Providing a String is not
  required - you may use a real function instead.
  
  For example - suppose you wanted to override the leafClick() method on
  the TreeGrid.  Normally you would do so as follows:
 
  
  TreeGrid.create({
      ...
      leafClick : function(viewer, leaf, recordNum) { 
          if(leaf.name == 'zoo') { 
              alert(1); 
          } else {
              alert(2);
          }
      }
  });
  
 
 Since leafClick is a StringMethod, however, you can shorten
 this to:
  TreeGrid.create({
      ...
      leafClick : "if(leaf.name == 'zoo') { alert(1); } else { alert(2); }";
  });