(Syntax Table Internals): Elaborate documentation of

syntax-after and syntax-class.

1 files changed, 16 insertions, 2 deletions

diff --git a/lispref/syntax.texi b/lispref/syntax.texi
index 7aa78aebf01..248ed77c4e9 100644
--- a/lispref/syntax.texi
+++ b/lispref/syntax.texi
@@ -940,11 +940,25 @@ This function returns the internal form @code{(@var{syntax-code} .
 @defun syntax-after pos
 This function returns the syntax code of the character in the buffer
 after position @var{pos}, taking account of syntax properties as well
-as the syntax table.
+as the syntax table.  If @var{pos} is outside the buffer's accessible
+portion (@pxref{Narrowing, accessible portion}), this function returns
+@code{nil}.
 @end defun
 
 @defun syntax-class syntax
-This function returns the syntax class of a syntax code.
+This function returns the syntax class of the syntax code
+@var{syntax}.  (It masks off the high 16 bits that hold the flags
+encoded in the syntax descriptor.)  If @var{syntax} is @code{nil}, it
+returns @code{nil}; this is so evaluating the expression
+
+@example
+(syntax-class (syntax-after pos))
+@end example
+
+@noindent
+where @code{pos} is outside the buffer's accessible portion, will
+yield @code{nil} without throwing errors or producing wrong syntax
+class codes.
 @end defun
 
 @node Categories