How to use zend search class with advsearch snippet in modx revo?

Question

MODX

The advsearch documentation says that you can use the Zend search class. I put the required files in the assets/libraries folder, however, when specified in the &engine=`zend` snippet call, 0 results are returned regardless of the request. The documentation says that you need to somehow index the resources. How can this be done?