V6/usr/doc/yacc/ssc

.SH
Appendix C: Old Features Supported but not Encouraged
.PP
This appendix mentions synonyms and features which are supported for historical
continuity, but, for various reasons, are not encouraged.
.IP 1.
Literals may be delimited by double quotes ``"'' as well as single quotes ``\'''.
.IP 2.
Literals may be more than one character long.
If all the characters are alphabetic, numeric, or \_, the type number of the literal is defined,
just as if the literal did not have the quotes around it.
Otherwise, it is difficult to find the value for such literals.
.IP
The use of multi-character literals is likely to mislead those unfamiliar with
Yacc, since it suggests that Yacc is doing a job which must be actually done by the lexical analyzer.
.IP 3.
Most places where % is legal, backslash ``\e'' may be used.
In particular, \e\e is the same as %%, \eleft the same as %left, etc.
.IP 4.
There are a number of other synonyms:
.DS
%< is the same as %left
%> is the same as %right
%binary and %2 are the same as %nonassoc
%0 and %term are the same as %token
%= is the same as %prec
.DE
.IP 5.
The curly braces ``{'' and ``}'' around an action are optional if the action consists of
a single C statement.
(They are always required in Ratfor).
.bp