-gd C code is inserted in each of the antlr generated parsing functions to provide for user-defined
handling of a detailed parse trace. The inserted code consists of calls to the user-supplied
macros or functions called zzTRACEIN and zzTRACEOUT. The only argument is a char * pointing to a
C-style string which is the grammar rule recognized by the current parsing function. If no
definition is given for the trace functions, upon rule entry and exit, a message will be printed
indicating that a particular rule as been entered or exited.