(Function Documentation): Explain how to

show calling convention explicitly in the doc string.

lispref/functions.texi

@@ -411,7 +411,7 @@ of one or two complete sentences that summarize the function's purpose.
 but since these spaces come before the starting double-quote, they are not part of
 the string.  Some people make a practice of indenting any additional
 lines of the string so that the text lines up in the program source.
-@emph{This is a mistake.}  The indentation of the following lines is
+@emph{That is a mistake.}  The indentation of the following lines is
 inside the string; what looks nice in the source code will look ugly
 when displayed by the help commands.
 
@@ -423,6 +423,19 @@ practice, there is no confusion between the first form of the body and the
 documentation string; if the only body form is a string then it serves both
 as the return value and as the documentation.
 
+  The last line of the documentation string can specify calling
+conventions different from the actual function arguments.  Write
+text like this:
+
+@example
+(fn @var{arglist})
+@end example
+
+@noindent
+following a blank line, with no newline following it inside the
+documentation string.  This feature is particularly useful for
+macro definitions.
+
 @node Function Names
 @section Naming a Function
 @cindex function definition