``` private rule_start ::= modifier* id '::=' ``` https://code.google.com/p/r4intellij/source/browse/gramgen/BnfAdaptedGrammar.bnf?r=3968eb3562d29456354233cb7b0c42cec5521502 http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form
