Reflection is a programming concept that sounds scarier than it is. There are three related concepts that fall under the umbrella of reflection, and I’ll be surprised if you haven’t come across most of these code ideas already, even if you didn’t know it was called reflection. The first concept is examination of your variables. 
Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).
