-@code{YYDEBUG} when you compile the parser. You could use
-@samp{-DYYDEBUG=1} as a compiler option or you could put @samp{#define
-YYDEBUG 1} in the C declarations section of the grammar file
-(@pxref{C Declarations, ,The C Declarations Section}). Alternatively, use the @samp{-t} option when
-you run Bison (@pxref{Invocation, ,Invoking Bison}). We always define @code{YYDEBUG} so that
-debugging is always possible.
+@code{YYDEBUG} to a nonzero value when you compile the parser. You
+could use @samp{-DYYDEBUG=1} as a compiler option or you could put
+@samp{#define YYDEBUG 1} in the C declarations section of the grammar
+file (@pxref{C Declarations, ,The C Declarations Section}).
+Alternatively, use the @samp{-t} option when you run Bison
+(@pxref{Invocation, ,Invoking Bison}) or the @code{%debug} declaration
+(@pxref{Decl Summary, ,Bison Declaration Summary}). We suggest that
+you always define @code{YYDEBUG} so that debugging is always possible.