This reverts to the behavior of Bison 1.33 and earlier, and improves
    compatibility with Yacc.

  - "parse error" -> "syntax error"
    Bison now uniformly uses the term "syntax error"; formerly, the code
    and manual sometimes used the term "parse error" instead.  POSIX
    requires "syntax error" in diagnostics, and it was thought better to
    be consistent.

  - The documentation now emphasizes that yylex and yyerror must be
    declared before use.  C99 requires this.

  - Bison now parses C99 lexical constructs like UCNs and
    backslash-newline within C escape sequences, as POSIX 1003.1-2001 requires.

  - File names are properly escaped in C output.  E.g., foo\bar.y is
    output as "foo\\bar.y".

  - Yacc command and library now available
    The Bison distribution now installs a "yacc" command, as POSIX requires.
    Also, Bison now installs a small library liby.a containing
    implementations of Yacc-compatible yyerror and main functions.
    This library is normally not useful, but POSIX requires it.

  - Type clashes now generate warnings, not errors.

  - If the user does not define YYSTYPE as a macro, Bison now declares it
    using typedef instead of defining it as a macro.
    For consistency, YYLTYPE is also declared instead of defined.

** Other compatibility issues

  - %union directives can now have a tag before the "{", e.g., the
    directive "%union foo {...}" now generates the C code
    "typedef union foo { ... } YYSTYPE;"; this is for Yacc compatibility.
    The default union tag is "YYSTYPE", for compatibility with Solaris 9 Yacc.
    For consistency, YYLTYPE's struct tag is now "YYLTYPE" not "yyltype".
    This is for compatibility with both Yacc and Bison 1.35.

  - ";" is output before the terminating "}" of an action, for
    compatibility with Bison 1.35.

  - Bison now uses a Yacc-style format for conflict reports, e.g.,
    "conflicts: 2 shift/reduce, 1 reduce/reduce".

  - "yystype" and "yyltype" are now obsolescent macros instead of being
    typedefs or tags; they are no longer documented and are planned to be
    withdrawn in a future release.

** GLR parser notes

  - GLR and inline
    Users of Bison have to decide how they handle the portability of the
    C keyword "inline".

  - "parsing stack overflow..." -> "parser stack overflow"
    GLR parsers now report "parser stack overflow" as per the Bison manual.

** %parse-param and %lex-param
  The macros YYPARSE_PARAM and YYLEX_PARAM provide a means to pass
  additional context to yyparse and yylex.  They suffer from several
  shortcomings:

  - a single argument only can be added,
  - their types are weak (void *),
  - this context is not passed to ancillary functions such as yyerror,
  - only yacc.c parsers support them.

  The new %parse-param/%lex-param directives provide a more precise control.
  For instance:

    %parse-param {int *nastiness}
    %lex-param   {int *nastiness}
    %parse-param {int *randomness}

  results in the following signatures:

    int yylex   (int *nastiness);
    int yyparse (int *nastiness, int *randomness);

  or, if both %pure-parser and %locations are used:

    int yylex   (YYSTYPE *lvalp, YYLTYPE *llocp, int *nastiness);
    int yyparse (int *nastiness, int *randomness);

** Bison now warns if it detects conflicting outputs to the same file,
  e.g., it generates a warning for "bison -d -o foo.h foo.y" since
  that command outputs both code and header to foo.h.

** #line in output files
  - --no-line works properly.

** Bison can no longer be built by a K&R C compiler; it requires C89 or
  later to be built.  This change originally took place a few versions
  ago, but nobody noticed until we recently asked someone to try
  building Bison with a K&R C compiler.