antlr-help-rules-intro is a variable defined in `antlr-mode.el'.
Its value is

"The following Makefile rules define the dependencies for all (non-\nexpanded) grammars in directory \"%s\".\n\nThey are stored in the kill-ring, i.e., you can insert them with C-y\ninto your Makefile. You can also invoke M-x antlr-show-makefile-rules\nfrom within a Makefile to insert them directly.\n\n\n"

Introduction to use with M-x antlr-show-makefile-rules.
It is a format string and used with substitution DIRECTORY/%s where
DIRECTORY is the name of the current directory.