Syntax definitions are valid only at the top level of a <program>.
They have the following form: (define-syntax <keyword> <transformer spec>)
<Keyword> is an identifier, and
the <transformer spec> should be an instance of syntax-rules.
The top-level syntactic environment is extended by binding the
<keyword> to the specified transformer.
There is no define-syntax analogue of internal definitions.
Although macros may expand into definitions and syntax definitions in any context that permits them, it is an error for a definition or syntax definition to shadow a syntactic keyword whose meaning is needed to determine whether some form in the group of forms that contains the shadowing definition is in fact a definition, or, for internal definitions, is needed to determine the boundary between the group and the expressions that follow the group. For example, the following are errors:
(define define 3)
(begin (define begin list))
(let-syntax
((foo (syntax-rules ()
((foo (proc args ...) body ...)
(define proc
(lambda (args ...)
body ...))))))
(let ((x 3))
(foo (plus x y) (+ x y))
(define foo x)
(plus foo x)))