--- a/etc/NEWS.9.md	Thu Nov 17 14:12:57 2022 -0800
+++ b/etc/NEWS.9.md	Thu Nov 17 14:48:19 2022 -0800
@@ -54,6 +54,18 @@
         .**      | .^
         .**=     | .^=
 
+- Interpreter
+
+    * The use of `'...'` for line continuations *inside* double-quoted
+    strings has been removed.  Use `'\'` for line continuations inside strings
+    instead.
+
+    * The use of `'\'` as a line continuation *outside* of double-quoted
+    strings has been removed.  Use `'...'` for line continuations instead.
+
+    * Support for trailing whitespace after a `'\'` line continuation has been
+    removed.  Delete unnecessary trailing whitespace.
+
 - For plot functions, the use of numbers to select line colors in
   shorthand formats was an undocumented feature was removed from Octave 9.
 

--- a/libinterp/parse-tree/lex.ll	Thu Nov 17 14:12:57 2022 -0800
+++ b/libinterp/parse-tree/lex.ll	Thu Nov 17 14:48:19 2022 -0800
@@ -1066,28 +1066,6 @@
     curr_lexer->m_string_text += '\v';
   }
 
-<DQ_STRING_START>(\.\.\.){S}*{NL} {
-    curr_lexer->lexer_debug ("<DQ_STRING_START>(\\.\\.\\.){S}*{NL}");
-
-    /* FIXME: Remove support for '...' continuation in Octave 9 */
-    static const char *msg = "'...' continuations in double-quoted character strings were deprecated in version 7 and will not be allowed in a future version of Octave; please use '\\' instead";
-
-    curr_lexer->warn_deprecated_syntax (msg);
-
-    HANDLE_STRING_CONTINUATION;
-  }
-
-<DQ_STRING_START>\\{S}+{NL} {
-    curr_lexer->lexer_debug ("<DQ_STRING_START>\\\\{S}+{NL}");
-
-    /* FIXME: Remove support for WS after line continuation in Octave 9 */
-    static const char *msg = "whitespace after continuation markers in double-quoted character strings were deprecated in version 7 and will not be allowed in a future version of Octave";
-
-    curr_lexer->warn_deprecated_syntax (msg);
-
-    HANDLE_STRING_CONTINUATION;
-  }
-
 <DQ_STRING_START>\\{NL} {
     curr_lexer->lexer_debug ("<DQ_STRING_START>\\\\{NL}");
 
@@ -1280,17 +1258,6 @@
 // Deprecated C preprocessor style continuation markers.
 %}
 
-\\{S}*{NL} |
-\\{S}*{CCHAR}{ANY_EXCEPT_NL}*{NL} {
-    curr_lexer->lexer_debug ("\\\\{S}*{NL}|\\\\{S}*{CCHAR}{ANY_EXCEPT_NL}*{NL}");
-
-    /* FIXME: Remove support for '\\' line continuation in Octave 9 */
-    static const char *msg = "using continuation marker \\ outside of double quoted strings was deprecated in version 7 and will be removed from a future version of Octave, use ... instead";
-
-    curr_lexer->warn_deprecated_syntax (msg);
-
-    curr_lexer->handle_continuation ();
-  }
 
 %{
 // End of file.

--- a/test/line-continue.tst	Thu Nov 17 14:12:57 2022 -0800
+++ b/test/line-continue.tst	Thu Nov 17 14:48:19 2022 -0800
@@ -33,34 +33,6 @@
 %! b];
 %! assert (y, x);
 
-## FIXME: Next 3 tests use '\' continuation outside of a double-quoted string
-##        This behavior is deprecated and will be removed at some point.
-##        When it does these
-%!test
-%! x = [1;2];
-%! y = [a... # comments here ok
-%! ;\
-%!
-%! b];
-%! assert (y, x);
-
-%!assert (1 + ...
-%! 2 - \# comments here ok
-%! 3 / ... # comments here ok
-%! -1,6);
-
-%!function y = f (a,...
-%!                b,  ...
-%!                c,  ...   % comments ok
-%!                x,  # continuation characters not required in parens
-%!                y,  \# but they should work too.
-%!                z)
-%!
-%!  y = 1;
-%!endfunction
-%!
-%!assert (f (), 1)
-
 ## String continuation using '\'
 %!assert (["abc\
 %! def"], "abc def")