Divided into a target and data for the target
The target must be an XML name
The data can have an effectively arbitrary format
<?robots index="yes" follow="no"?>
<?xml-stylesheet href="pelicans.css" type="text/css"?>
<?php 
  mysql_connect("database.unc.edu", "clerk", "password"); 
  $result = mysql("CYNW", "SELECT LastName, FirstName FROM Employees 
    ORDER BY LastName, FirstName"); 
  $i = 0;
  while ($i < mysql_numrows ($result)) {
     $fields = mysql_fetch_row($result);
     echo "<person>$fields[1] $fields[0] </person>\r\n";
     $i++;
  }
  mysql_close();
?>
These are for programs