Helper class invoked just after StageTwoParser. Its job is to create variables referenced by labels (label:item) and by code blocks ($RuleName), to modify the code blocks to remove the $ operator, and to update the ResultSaver of each labeled predicate. Also supports $result.
Labels and $substitutions can also be used with Preds constructed by hand, except that referencing tokens directly from code blocks (e.g. $'#') won't work unless the corresponding grammar Pred has a Pred.Basis is an equal syntax tree.