A convention is used to present attribution rules more concisely, by making
computation of "boilerplate" values for attributes implicit:
If a production has exactly one child node in the AST, then its
boilerplate attribute values are given by the attributes of that child.
A subclass of ANTLRStringStream with the following customizations:
As each char is consumed, check whether it and the immediately
preceding chars violate the FILTER_CDATA rule of the Jacaranda