document.observe("dom:loaded", function() {
  var table = new Element("table");
  var row = new Element("tr");
  row.insert(new Element("td").update("foo"));
  row.insert(new Element("td").update("bar"));
  table.insert(row);
  $(document.body).insert(table);
});

document.observe("dom:loaded", function() {
  var table = new Element("table");
  var thead = new Element("thead");
  var row = new Element("tr");
  row.insert(new Element("td").update("foo"));
  row.insert(new Element("td").update("bar"));
  thead.insert(row);
  table.insert(thead);
  $(document.body).insert(table);
});