+In some cases the Bison parser file includes system headers, and in
+those cases your code should respect the identifiers reserved by those
+headers. On some non-@sc{gnu} hosts, @code{<alloca.h>},
+@code{<stddef.h>}, and @code{<stdlib.h>} are included as needed to
+declare memory allocators and related types. On all hosts,
+@code{<stdio.h>} is included if you define @code{YYDEBUG}
+(@pxref{Debugging, ,Debugging Your Parser}).
+