How can the issue of variable substitution within the XML code be resolved in PHP?
Issue: Variable substitution within XML code can be resolved in PHP by using the `sprintf` function to format the XML code with the variables.
// Variables to be substituted in the XML code
$name = "John";
$age = 30;
// XML code with placeholders for variables
$xml = '<person><name>%s</name><age>%d</age></person>';
// Format the XML code with the variables
$formatted_xml = sprintf($xml, $name, $age);
echo $formatted_xml;