Document that `buffer-string' retains text properties

* doc/lispref/text.texi (Buffer Contents): Mention text properties
in the `buffer-string' documentation.
* src/editfns.c (Fbuffer_string): Mention text properties in the
doc string (bug#47220).

doc/lispref/text.texi

@@ -222,7 +222,9 @@ properties, just the characters themselves.  @xref{Text Properties}.
 
 @defun buffer-string
 This function returns the contents of the entire accessible portion of
-the current buffer, as a string.
+the current buffer, as a string.  If the text being copied has any
+text properties, these are copied into the string along with the
+characters they belong to.
 @end defun
 
   If you need to make sure the resulting string, when copied to a

src/editfns.c

@@ -1697,7 +1697,11 @@ they can be in either order.  */)
 DEFUN ("buffer-string", Fbuffer_string, Sbuffer_string, 0, 0, 0,
        doc: /* Return the contents of the current buffer as a string.
 If narrowing is in effect, this function returns only the visible part
-of the buffer.  */)
+of the buffer.
+
+This function copies the text properties of that part of the buffer
+into the result string; if you don’t want the text properties,
+use `buffer-substring-no-properties' instead.  */)
   (void)
 {
   return make_buffer_string_both (BEGV, BEGV_BYTE, ZV, ZV_BYTE, 1);