向谷歌地图添加标记:WordPress和XML

I'm following this tutorial on placing markers on a Google Map using PHP and MySQL. I'm adapting it to work in a WordPress Shortcode plugin. I've built the map and pulled the lat longs from the database. I'm having problems figuring out how to get WordPress to output XML, (which will then be used by javascript to place the markers). This is a snippet of my plugin: on placing markers