The rules borrow from many sources, including numerous style guides that the first author re-read in preparation of writing this document. The first author also conducted focus sessions with the members of PLT at various sites, and these sessions produced many insights about coding style. Thank you to everyone for sitting through these sessions and for reading early drafts of the style guide. Eli Barzilay and Jacob Matthews took the time to write up their thoughts on various issues, and their help is much appreciated. Rouben Rostamian spotted some problems in an early draft of the report.