Don't document %no-default-prec for now.

doc/bison.texinfo

@@ -16,6 +16,10 @@
 @c @clear shorttitlepage-enabled
 @c @set shorttitlepage-enabled
 
+@c Set following if you want to document %default-prec and %no-default-prec.
+@c This feature is experimental and may change in future Bison versions.
+@c @set defaultprec
+
 @c ISPELL CHECK: done, 14 Jan 1993 --bob
 
 @c Check COPYRIGHT dates.  should be updated in the titlepage, ifinfo
@@ -3684,10 +3688,12 @@ Declare a terminal symbol (token type name) that is nonassociative
 Using it in a way that would be associative is a syntax error.
 @end deffn
 
+@ifset defaultprec
 @deffn {Directive} %default-prec
 Assign a precedence to rules lacking an explicit @code{%prec} modifier
 (@pxref{Contextual Precedence, ,Context-Dependent Precedence}).
 @end deffn
+@end ifset
 
 @deffn {Directive} %type
 Declare the type of semantic values for a nonterminal symbol
@@ -3759,11 +3765,13 @@ and so on.  @xref{Multiple Parsers, ,Multiple Parsers in the Same
 Program}.
 @end deffn
 
+@ifset defaultprec
 @deffn {Directive} %no-default-prec
 Do not assign a precedence to rules lacking an explicit @code{%prec}
 modifier (@pxref{Contextual Precedence, ,Context-Dependent
 Precedence}).
 @end deffn
+@end ifset
 
 @deffn {Directive} %no-parser
 Do not include any C code in the parser file; generate tables only.  The
@@ -4863,6 +4871,7 @@ exp:    @dots{}
 @end group
 @end example
 
+@ifset defaultprec
 If you forget to append @code{%prec UMINUS} to the rule for unary
 minus, Bison silently assumes that minus has its usual precedence.
 This kind of problem can be tricky to debug, since one typically
@@ -4882,6 +4891,7 @@ grammar, but it helps to protect against incorrect rule precedences.
 
 The effect of @code{%no-default-prec;} can be reversed by giving
 @code{%default-prec;}, which is the default.
+@end ifset
 
 @node Parser States
 @section Parser States
@@ -6814,11 +6824,13 @@ parsing.  @xref{Parser Function, ,The Parser Function @code{yyparse}}.
 Equip the parser for debugging.  @xref{Decl Summary}.
 @end deffn
 
+@ifset defaultprec
 @deffn {Directive} %default-prec
 Assign a precedence to rules that lack an explicit @samp{%prec}
 modifier.  @xref{Contextual Precedence, ,Context-Dependent
 Precedence}.
 @end deffn
+@end ifset
 
 @deffn {Directive} %defines
 Bison declaration to create a header file meant for the scanner.
@@ -6873,11 +6885,13 @@ function is applied to the two semantic values to get a single result.
 Bison declaration to rename the external symbols.  @xref{Decl Summary}.
 @end deffn
 
+@ifset defaultprec
 @deffn {Directive} %no-default-prec
 Do not assign a precedence to rules that lack an explicit @samp{%prec}
 modifier.  @xref{Contextual Precedence, ,Context-Dependent
 Precedence}.
 @end deffn
+@end ifset
 
 @deffn {Directive} %no-lines
 Bison declaration to avoid generating @code{#line} directives in the