JD Long (at Cerebral Mastication) posted a question on Twitter about an artifact in ESS, where typing “_” gets you “<-”. This is because in the early days of S+, “_” was an allowed assignment operator, and ESS was developed in that era. Later, it was disallowed in favor of “<-” and “=”, so ESS 





Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).