Update release/unstable with recent changes

16 files changed, 292 insertions, 119 deletions

diff --git a/Documentation/changes.tely b/Documentation/changes.tely
index fb1a77f633..c9315d59da 100644
--- a/Documentation/changes.tely
+++ b/Documentation/changes.tely
@@ -62,6 +62,25 @@ which scares away people.
 @end ignore
 
 @item
+Slurs and phrasing slurs may now be started from individual notes
+in a chord.  Several simultanous slurs per @code{Voice} need to be
+distinguished by @code{spanner-id} setting.
+
+@item
+The music and grob property @code{spanner-id} for distinguishing
+simultaneous slurs and phrasing slurs has been changed from a
+string to a @q{key}, a non-negative integer or symbol.
+
+@item
+There is a new command @code{\=} for specifying the
+@code{spanner-id} for simultaneous slurs and phrasing slurs.
+@lilypond[verbatim,quote]
+\fixed c' {
+  <c~ f\=1( g\=2( >2 <c e\=1) a\=2) >
+}
+@end lilypond
+
+@item
 Blocks introduced with @code{\header} can be stored in variables
 and used as arguments to music and scheme functions and as the
 body of @code{#@{@dots{}#@}} constructs.  They are represented as
diff --git a/Documentation/contributor/programming-work.itexi b/Documentation/contributor/programming-work.itexi
index 4b0b43dad4..8dc8d2755b 100644
--- a/Documentation/contributor/programming-work.itexi
+++ b/Documentation/contributor/programming-work.itexi
@@ -367,40 +367,35 @@ If you like using font-lock, you can also add this to your
 @end example
 
 
-@subheading Indenting with vim
-
-Although emacs indentation is the GNU standard, acceptable
-indentation can usually be accomplished with vim.  Some hints for
-vim are as follows:
-
-A workable .vimrc:
-
-@example
-set cindent
-set smartindent
-set autoindent
-set expandtab
-set softtabstop=2
-set shiftwidth=2
-filetype plugin indent on
-set incsearch
-set ignorecase smartcase
-set hlsearch
-set confirm
-set statusline=%F%m%r%h%w\ %@{&ff@}\ %Y\ [ASCII=\%03.3b]\ [HEX=\%02.2B]\ %04l,%04v\ %p%%\ [LEN=%L]
-set laststatus=2
-set number
-" Remove trailing whitespace on write
+@subsubheading Indenting with vim
+
+Although emacs indentation is the GNU standard, correct
+indentation for C++ files can be achieved by using the settings
+recommended in the
+@url{https://gcc.gnu.org/wiki/FormattingCodeForGCC, GNU GCC Wiki}.
+Save the following in @file{~/.vim/after/ftplugin/cpp.vim}:
+
+@example
+setlocal cindent
+setlocal cinoptions=>4,n-2,@{2,^-2,:2,=2,g0,h2,p5,t0,+2,(0,u0,w1,m1
+setlocal shiftwidth=2
+setlocal softtabstop=2
+setlocal textwidth=79
+setlocal fo-=ro fo+=cql
+" use spaces instead of tabs
+setlocal expandtab
+" remove trailing whitespace on write
 autocmd BufWritePre * :%s/\s\+$//e
 @end example
 
-With this @file{.vimrc}, files can be reindented automatically by
+With these settings, files can be reindented automatically by
 highlighting the lines to be indented in visual mode (use V to
-enter visual mode) and pressing @code{=}.
+enter visual mode) and pressing @code{=}, or a single line
+correctly indented in normal mode by pressing @code{==}.
 
-A @file{scheme.vim} file will help improve the indentation.  This
-one was suggested by Patrick McCarty.  It should be saved in
-@file{~/.vim/after/syntax/scheme.vim}.
+A @file{scheme.vim} file will help improve the indentation of
+Scheme code.  This one was suggested by Patrick McCarty.  It
+should be saved in @file{~/.vim/after/syntax/scheme.vim}.
 
 @example
 " Additional Guile-specific 'forms'
@@ -417,24 +412,45 @@ syn keyword schemeSyntax define-safe-public define-music-function
 syn keyword schemeSyntax def-grace-function
 
 " All of the above should influence indenting too
-set lw+=define-public,define*-public
-set lw+=define*,lambda*,let-keywords*
-set lw+=defmacro,defmacro*,define-macro
-set lw+=defmacro-public,defmacro*-public
-set lw+=use-modules,define-module
-set lw+=define-method,define-class
-set lw+=define-markup-command,define-markup-list-command
-set lw+=define-safe-public,define-music-function
-set lw+=def-grace-function
+setlocal lw+=define-public,define*-public
+setlocal lw+=define*,lambda*,let-keywords*
+setlocal lw+=defmacro,defmacro*,define-macro
+setlocal lw+=defmacro-public,defmacro*-public
+setlocal lw+=use-modules,define-module
+setlocal lw+=define-method,define-class
+setlocal lw+=define-markup-command,define-markup-list-command
+setlocal lw+=define-safe-public,define-music-function
+setlocal lw+=def-grace-function
 
 " These forms should not influence indenting
-set lw-=if
-set lw-=set!
+setlocal lw-=if
+setlocal lw-=set!
 
 " Try to highlight all ly: procedures
 syn match schemeFunc "ly:[^) ]\+"
 @end example
 
+For documentation work on texinfo files, identify the file
+extensions used as texinfo files in your @file{.vim/filetype.vim}:
+
+@example
+if exists("did_load_filetypes")
+  finish
+endif
+augroup filetypedetect
+  au! BufRead,BufNewFile *.itely setfiletype texinfo
+  au! BufRead,BufNewFile *.itexi setfiletype texinfo
+  au! BufRead,BufNewFile *.tely  setfiletype texinfo
+augroup END
+@end example
+
+and add these settings in @file{.vim/after/ftplugin/texinfo.vim}:
+
+@example
+setlocal expandtab
+setlocal shiftwidth=2
+setlocal textwidth=66
+@end example
 
 @node Naming conventions
 @subsection Naming Conventions
diff --git a/Documentation/notation/expressive.itely b/Documentation/notation/expressive.itely
index d3f0235246..3c249389c2 100644
--- a/Documentation/notation/expressive.itely
+++ b/Documentation/notation/expressive.itely
@@ -685,7 +685,8 @@ occurences of outer slurs actually indicate phrasing, and phrasing
 slurs may overlap a regular slur, see @ref{Phrasing slurs}.  When
 multiple regular slurs are needed in a single @code{Voice},
 matching slur starts and ends need to be labelled by preceding
-them with @code{\=} followed by an identifying number or string.
+them with @code{\=} followed by an identifying key (a symbol or
+non-negative integer).
 
 @lilypond[verbatim,quote]
 \fixed c' {
diff --git a/Documentation/notation/pitches.itely b/Documentation/notation/pitches.itely
index 0699239db5..bfed32447e 100644
--- a/Documentation/notation/pitches.itely
+++ b/Documentation/notation/pitches.itely
@@ -903,9 +903,14 @@ music = \relative { c'8. ees16( fis8. a16 b8.) gis16 f8. d16 }
 @end lilypond
 
 @knownissues
-Manual ties inside @code{\retrograde} will be broken and
-generate warnings.  Some ties can be generated automatically
-by enabling @ref{Automatic note splitting}.
+@code{\retrograde} is a rather simple tool.  Since many events are
+@q{mirrored} rather than exchanged, tweaks and directional
+modifiers for opening spanners need to be added at the matching
+closing spanners: @code{^(} needs to be ended by @code{^)}, every
+@code{\<} or @code{\cresc} needs to be ended by @code{\!} or
+@code{\endcr}, every @code{\>} or @code{\decr} needs to be ended
+by @code{\enddecr}.  Property-changing commands/overrides with a
+lasting effect will likely cause surprises.
 
 @seealso
 Notation Reference:
diff --git a/input/regression/retrograde.ly b/input/regression/retrograde.ly
new file mode 100644
index 0000000000..dd7f7eba95
--- /dev/null
+++ b/input/regression/retrograde.ly
@@ -0,0 +1,30 @@
+\version "2.18.0"
+
+\header {
+  texidoc = "@code{\\retrograde} can deal with crescendo and
+  decrescendo as long as they are properly paired with
+  @code{\\endcr}/@code{\\!} and @code{\\enddecr}.  Direction modifiers
+  on slurs like @code{^(} need to be repeated as @code{^)} at the end.
+  Ties and glissandi work mostly (in-chord ties are turned into
+  ordinary per-chord/note ties, however)."
+}
+
+\layout { ragged-right = ##t }
+
+motif =
+\relative {
+  \override TextSpanner.bound-details.left.text = "motif"
+  <c' e>2~\startTextSpan  c16\< d^( e f~ f4:32^)\!\> |
+  <<
+    \context Voice = "voice" {
+      <g~ b>4 g8\glissando f\stopTextSpan\enddecr }
+    \\
+    { c2 }
+  >>
+}
+
+\new Voice = "voice" {
+  \motif
+  \override TextSpanner.bound-details.left.text = "retrograde motif"
+  \retrograde  \motif \bar "|."
+}
diff --git a/lily/include/slur-engraver.hh b/lily/include/slur-engraver.hh
index 572e7ea023..1885625ed9 100644
--- a/lily/include/slur-engraver.hh
+++ b/lily/include/slur-engraver.hh
@@ -60,8 +60,8 @@ protected:
   void stop_translation_timestep ();
   void process_music ();
 
-  bool can_create_slur (const string&, vsize, vsize *, Stream_event *);
-  void create_slur (const string &spanner_id, Event_info evi, Grob *g_cause, Direction dir, bool left_broken);
+  bool can_create_slur (SCM, vsize, vsize *, Stream_event *);
+  void create_slur (SCM spanner_id, Event_info evi, Grob *g_cause, Direction dir, bool left_broken);
   bool try_to_end (Event_info evi);
 
   virtual void set_melisma (bool);
diff --git a/lily/parser.yy b/lily/parser.yy
index 159786b93c..83e95491c2 100644
--- a/lily/parser.yy
+++ b/lily/parser.yy
@@ -229,7 +229,7 @@ static Music *make_music_with_input (SCM name, Input where);
 SCM check_scheme_arg (Lily_parser *parser, Input loc,
 		      SCM arg, SCM args, SCM pred, SCM disp = SCM_UNDEFINED);
 SCM make_music_from_simple (Lily_parser *parser, Input loc, SCM pitch);
-SCM loc_on_music (Lily_parser *parser, Input loc, SCM arg);
+SCM loc_on_copy (Lily_parser *parser, Input loc, SCM arg);
 SCM make_chord_elements (Input loc, SCM pitch, SCM dur, SCM modification_list);
 SCM make_chord_step (SCM step, Rational alter);
 SCM make_simple_markup (SCM a);
@@ -500,8 +500,8 @@ lookup:
 	LOOKUP_IDENTIFIER
 	| LOOKUP_IDENTIFIER '.' symbol_list_rev
 	{
-		$$ = loc_on_music (parser, @$,
-				   nested_property ($1, scm_reverse_x ($3, SCM_EOL)));
+		$$ = loc_on_copy (parser, @$,
+				  nested_property ($1, scm_reverse_x ($3, SCM_EOL)));
 	}
 	;
 
@@ -1992,7 +1992,7 @@ function_arglist_backup:
 				$$ = scm_cons ($$, $3);
 			else
 			{
-				$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+				$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 				MYBACKUP (SCM_ARG, $4, @4);
 			}
 		}
@@ -2003,7 +2003,7 @@ function_arglist_backup:
 		{
 			$$ = scm_cons ($4, $3);
 		} else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (EVENT_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2019,7 +2019,7 @@ function_arglist_backup:
 		} else if (scm_is_true (scm_call_1 ($2, $4)))
 			$$ = scm_cons ($4, $3);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (PITCH_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2035,7 +2035,7 @@ function_arglist_backup:
 		} else if (scm_is_true (scm_call_1 ($2, $4)))
 			$$ = scm_cons ($4, $3);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (TONICNAME_PITCH, $4, @4);
 		}
 	}
@@ -2044,7 +2044,7 @@ function_arglist_backup:
 		if (scm_is_true (scm_call_1 ($2, $4)))
 			$$ = scm_cons ($4, $3);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (SCM_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2066,11 +2066,11 @@ function_arglist_backup:
 					  ($2, make_music_from_simple (parser, @4, d))))
 					MYREPARSE (@4, $2, DURATION_ARG, d);
 				else {
-					$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+					$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 					MYBACKUP (UNSIGNED, $4, @4);
 				}
 			} else {
-				$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+				$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 				MYBACKUP (UNSIGNED, $4, @4);
 			}
 		}
@@ -2082,7 +2082,7 @@ function_arglist_backup:
 			$$ = $3;
 			MYREPARSE (@4, $2, REAL, $4);
 		} else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (REAL, $4, @4);
 		}
 	}
@@ -2092,7 +2092,7 @@ function_arglist_backup:
 		{
 			$$ = scm_cons ($4, $3);
 		} else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (NUMBER_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2109,7 +2109,7 @@ function_arglist_backup:
 			if (scm_is_true (scm_call_1 ($2, $$)))
 				$$ = scm_cons ($$, $3);
 			else {
-				$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+				$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 				MYBACKUP (UNSIGNED, $5, @5);
 				parser->lexer_->push_extra_token (@4, '-');
 			}
@@ -2122,7 +2122,7 @@ function_arglist_backup:
 			MYREPARSE (@5, $2, REAL, n);
 			$$ = $3;
 		} else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (REAL, n, @5);
 		}
 	}
@@ -2132,7 +2132,7 @@ function_arglist_backup:
 		if (scm_is_true (scm_call_1 ($2, n))) {
 			$$ = scm_cons (n, $3);
 		} else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (NUMBER_IDENTIFIER, n, @5);
 		}
 	}
@@ -2146,7 +2146,7 @@ function_arglist_backup:
 			  ($2, make_music_from_simple (parser, @4, $4))))
 			MYREPARSE (@4, $2, DURATION_ARG, $4);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (DURATION_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2161,7 +2161,7 @@ function_arglist_backup:
 			else
 				$$ = scm_cons (res, $3);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (SCM_IDENTIFIER, $4, @4);
 		}
 	}
@@ -2176,7 +2176,7 @@ function_arglist_backup:
 			else
 				$$ = scm_cons (res, $3);
 		else {
-			$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+			$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 			MYBACKUP (STRING, $4, @4);
 		}
 	}
@@ -2215,7 +2215,7 @@ function_arglist:
 	function_arglist_nonbackup
 	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_skip_nonbackup DEFAULT
 	{
-		$$ = scm_cons (loc_on_music (parser, @4, $1), $3);
+		$$ = scm_cons (loc_on_copy (parser, @4, $1), $3);
 	}
 	;
 
@@ -2223,7 +2223,7 @@ function_arglist_skip_nonbackup:
 	function_arglist_nonbackup
 	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_skip_nonbackup
 	{
-		$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+		$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 	}
 	;
 
@@ -2483,7 +2483,7 @@ function_arglist_optional:
 	function_arglist_backup
 	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_skip_backup DEFAULT
 	{
-		$$ = scm_cons (loc_on_music (parser, @4, $1), $3);
+		$$ = scm_cons (loc_on_copy (parser, @4, $1), $3);
 	}
 	| function_arglist_skip_backup BACKUP
 	;
@@ -2492,7 +2492,7 @@ function_arglist_skip_backup:
 	function_arglist_backup
 	| EXPECT_OPTIONAL EXPECT_SCM function_arglist_skip_backup
 	{
-		$$ = scm_cons (loc_on_music (parser, @3, $1), $3);
+		$$ = scm_cons (loc_on_copy (parser, @3, $1), $3);
 	}
 	;
 
@@ -4146,7 +4146,7 @@ SCM check_scheme_arg (Lily_parser *parser, Input loc,
 	return args;
 }
 
-SCM loc_on_music (Lily_parser *parser, Input loc, SCM arg)
+SCM loc_on_copy (Lily_parser *parser, Input loc, SCM arg)
 {
 	if (Music *m = unsmob<Music> (arg))
 	{
@@ -4154,6 +4154,34 @@ SCM loc_on_music (Lily_parser *parser, Input loc, SCM arg)
 		m->set_spot (parser->lexer_->override_input (loc));
 		return m->unprotect ();
 	}
+	if (Book *b = unsmob<Book> (arg))
+	{
+		b = b->clone ();
+		b->origin ()->set_spot (parser->lexer_->override_input (loc));
+		return b->unprotect ();
+	}
+	if (Context_def *cd = unsmob<Context_def> (arg))
+	{
+		cd = cd->clone ();
+		cd->origin ()->set_spot (parser->lexer_->override_input (loc));
+		return cd->unprotect ();
+	}
+	if (Output_def *od = unsmob<Output_def> (arg))
+	{
+		od = od->clone ();
+		od->input_origin_ = parser->lexer_->override_input (loc);
+		return od->unprotect ();
+	}
+	if (Score *s = unsmob<Score> (arg))
+	{
+		s = s->clone ();
+		s->origin ()->set_spot (parser->lexer_->override_input (loc));
+		return s->unprotect ();
+	}
+	if (Context_mod *cm = unsmob<Context_mod> (arg))
+	{
+		return cm->smobbed_copy ();
+	}
 	return arg;
 }
 
diff --git a/lily/slur-engraver.cc b/lily/slur-engraver.cc
index 1a06ca6422..80ceb5f431 100644
--- a/lily/slur-engraver.cc
+++ b/lily/slur-engraver.cc
@@ -189,14 +189,14 @@ Slur_engraver::finalize ()
 }
 
 void
-Slur_engraver::create_slur (const string &spanner_id, Event_info evi, Grob *g_cause, Direction dir, bool left_broken)
+Slur_engraver::create_slur (SCM spanner_id, Event_info evi, Grob *g_cause, Direction dir, bool left_broken)
 {
   Grob *ccc = left_broken
     ? unsmob<Grob> (get_property ("currentCommandColumn"))
     : 0; // efficiency
   SCM cause = evi.slur_ ? evi.slur_->self_scm () : g_cause->self_scm ();
   Spanner *slur = make_spanner (grob_symbol (), cause);
-  slur->set_property ("spanner-id", ly_string2scm (spanner_id));
+  slur->set_property ("spanner-id", spanner_id);
   if (dir)
     set_grob_direction (slur, dir);
   if (left_broken)
@@ -209,7 +209,7 @@ Slur_engraver::create_slur (const string &spanner_id, Event_info evi, Grob *g_ca
   {
     set_grob_direction (slur, DOWN);
     slur = make_spanner (grob_symbol (), cause);
-    slur->set_property ("spanner-id", ly_string2scm (spanner_id));
+    slur->set_property ("spanner-id", spanner_id);
     set_grob_direction (slur, UP);
     if (left_broken)
       slur->set_bound (LEFT, ccc);
@@ -221,7 +221,7 @@ Slur_engraver::create_slur (const string &spanner_id, Event_info evi, Grob *g_ca
 }
 
 bool
-Slur_engraver::can_create_slur (const string &id, vsize old_slurs, vsize *event_idx, Stream_event *ev)
+Slur_engraver::can_create_slur (SCM id, vsize old_slurs, vsize *event_idx, Stream_event *ev)
 {
   for (vsize j = slurs_.size (); j--;)
     {
@@ -229,7 +229,7 @@ Slur_engraver::can_create_slur (const string &id, vsize old_slurs, vsize *event_
       Direction updown = to_dir (ev->get_property ("direction"));
 
       // Check if we already have a slur with the same spanner-id.
-      if (id == robust_scm2string (slur->get_property ("spanner-id"), ""))
+      if (ly_is_equal (id, slur->get_property ("spanner-id")))
         {
           if (j < old_slurs)
             {
@@ -280,13 +280,13 @@ Slur_engraver::can_create_slur (const string &id, vsize old_slurs, vsize *event_
 bool
 Slur_engraver::try_to_end (Event_info evi)
 {
-  string id = robust_scm2string (evi.slur_->get_property ("spanner-id"), "");
+  SCM id = evi.slur_->get_property ("spanner-id");
 
   // Find the slurs that are ended with this event (by checking the spanner-id)
   bool ended = false;
   for (vsize j = slurs_.size (); j--;)
     {
-      if (id == robust_scm2string (slurs_[j]->get_property ("spanner-id"), ""))
+      if (ly_is_equal (id, slurs_[j]->get_property ("spanner-id")))
         {
           ended = true;
           end_slurs_.push_back (slurs_[j]);
@@ -305,16 +305,14 @@ Slur_engraver::process_music ()
 {
   for (vsize i = 0; i < stop_events_.size (); i++)
     {
-      string id = robust_scm2string
-        (stop_events_[i].slur_->get_property ("spanner-id"), "");
+      SCM id = stop_events_[i].slur_->get_property ("spanner-id");
       bool ended = try_to_end (stop_events_[i]);
       if (ended)
         {
           // Ignore redundant stop events for this id
           for (vsize j = stop_events_.size (); --j > i;)
             {
-              if (id == robust_scm2string
-                  (stop_events_[j].slur_->get_property ("spanner-id"), ""))
+              if (ly_is_equal (id, stop_events_[j].slur_->get_property ("spanner-id")))
                 stop_events_.erase (stop_events_.begin () + j);
             }
         }
@@ -326,7 +324,7 @@ Slur_engraver::process_music ()
   for (vsize i = start_events_.size (); i--;)
     {
       Stream_event *ev = start_events_[i].slur_;
-      string id = robust_scm2string (ev->get_property ("spanner-id"), "");
+      SCM id = ev->get_property ("spanner-id");
       Direction updown = to_dir (ev->get_property ("direction"));
 
       if (can_create_slur (id, old_slurs, &i, ev))
diff --git a/ly/grace-init.ly b/ly/grace-init.ly
index 6fe32f49fb..a46111e4d9 100644
--- a/ly/grace-init.ly
+++ b/ly/grace-init.ly
@@ -1,7 +1,7 @@
 \version "2.17.6"
 
-startGraceSlur = #(make-music 'SlurEvent 'span-direction START 'spanner-id "grace")
-stopGraceSlur = #(make-music 'SlurEvent 'span-direction STOP 'spanner-id "grace")
+startGraceSlur = #(make-music 'SlurEvent 'span-direction START 'spanner-id 'grace)
+stopGraceSlur = #(make-music 'SlurEvent 'span-direction STOP 'spanner-id 'grace)
 
 
 startGraceMusic =  {
diff --git a/ly/music-functions-init.ly b/ly/music-functions-init.ly
index ee9fdb8c20..76c2ec64b8 100644
--- a/ly/music-functions-init.ly
+++ b/ly/music-functions-init.ly
@@ -1551,7 +1551,12 @@ retrograde =
 #(define-music-function (music)
     (ly:music?)
     (_i "Return @var{music} in reverse order.")
-    (retrograde-music music))
+    (retrograde-music
+     (expand-repeat-notes!
+      (expand-repeat-chords!
+       (cons 'rhythmic-event
+             (ly:parser-lookup '$chord-repeat-events))
+       music))))
 
 revertTimeSignatureSettings =
 #(define-music-function
diff --git a/ly/spanners-init.ly b/ly/spanners-init.ly
index 756a55579e..8d8a69444f 100644
--- a/ly/spanners-init.ly
+++ b/ly/spanners-init.ly
@@ -1,18 +1,15 @@
 \version "2.19.29"
 
 "\\=" =
-#(define-event-function (id event) (number-or-string? ly:event?)
+#(define-event-function (id event) (key? ly:event?)
   (_i "This sets the @code{spanner-id} property of the following
-@var{event} to the given @var{id} (numbers will be converted to a
-string).  This can be used to tell LilyPond how to connect overlapping
+@var{event} to the given @var{id} (non-negative integer or symbol).
+This can be used to tell LilyPond how to connect overlapping
 or parallel slurs or phrasing slurs within a single @code{Voice}.
 @lilypond[quote,verbatim]
 \\fixed c' { c\\=1( d\\=2( e\\=1) f\\=2) }
 @end lilypond\n")
-  (set! (ly:music-property event 'spanner-id)
-	(if (number? id)
-	    (number->string id)
-	    id))
+  (set! (ly:music-property event 'spanner-id) id)
   event)
 
 startGroup = #(make-span-event 'NoteGroupingEvent START)
diff --git a/scm/define-grob-properties.scm b/scm/define-grob-properties.scm
index cb9103a6fc..7ca44b6f3d 100644
--- a/scm/define-grob-properties.scm
+++ b/scm/define-grob-properties.scm
@@ -992,7 +992,7 @@ override:
 \\override MultiMeasureRest
   #'spacing-pair = #'(staff-bar . staff-bar)
 @end example")
-     (spanner-id ,string? "An identifier to distinguish concurrent spanners.")
+     (spanner-id ,key? "An identifier to distinguish concurrent spanners.")
      (springs-and-rods ,boolean? "Dummy variable for triggering
 spacing routines.")
      (stacking-dir ,ly:dir? "Stack objects in which direction?")
diff --git a/scm/define-grobs.scm b/scm/define-grobs.scm
index f525edd69a..6ca25b586e 100644
--- a/scm/define-grobs.scm
+++ b/scm/define-grobs.scm
@@ -1787,7 +1787,6 @@
         (height-limit . 2.0)
         (minimum-length . 1.5)
         (ratio . 0.333)
-        (spanner-id . "")
         (springs-and-rods . ,ly:spanner::set-spacing-rods)
         (stencil . ,ly:slur::print)
         (thickness . 1.1)
@@ -1957,7 +1956,6 @@
         (line-thickness . 0.8)
         (minimum-length . 1.5)
         (ratio . 0.25)
-        (spanner-id . "")
         (springs-and-rods . ,ly:spanner::set-spacing-rods)
         (stencil . ,ly:slur::print)
         (thickness . 1.2)
diff --git a/scm/define-music-properties.scm b/scm/define-music-properties.scm
index 4df3f93340..f8c567d1fa 100644
--- a/scm/define-music-properties.scm
+++ b/scm/define-music-properties.scm
@@ -183,7 +183,7 @@ If zero, signals a beat containing varying durations.")
 Options are @code{'text} and @code{'hairpin}.")
      (span-text ,markup? "The displayed text for dynamic text
 spanners (e.g., cresc.)")
-     (spanner-id ,string? "Identifier to distinguish concurrent spanners.")
+     (spanner-id ,key? "Identifier to distinguish concurrent spanners.")
      (start-callback ,procedure? "Function to compute the negative length
 of starting grace notes.  This property can only be defined as initializer
 in @file{scm/@/define-music-types.scm}.")
diff --git a/scm/define-music-types.scm b/scm/define-music-types.scm
index e0190eda55..348bcd0e87 100644
--- a/scm/define-music-types.scm
+++ b/scm/define-music-types.scm
@@ -438,7 +438,6 @@ goes down).")
      . ((description . "Start or end phrasing slur.
 
 Syntax: @var{note}@code{\\(} and @var{note}@code{\\)}")
-        (spanner-id . "")
         (types . (post-event span-event event phrasing-slur-event))
         ))
 
@@ -570,7 +569,6 @@ Syntax: @code{\\skip} @var{duration}")
      . ((description . "Start or end slur.
 
 Syntax: @var{note}@code{(} and @var{note}@code{)}")
-        (spanner-id . "")
         (types . (post-event span-event event slur-event))
         ))
 
diff --git a/scm/modal-transforms.scm b/scm/modal-transforms.scm
index 98e9ac3021..f9e26ed360 100644
--- a/scm/modal-transforms.scm
+++ b/scm/modal-transforms.scm
@@ -185,32 +185,110 @@ Typically used to construct a scale for input to
 
 (define-public (retrograde-music music)
   "Returns @var{music} in retrograde (reversed) order."
-  ;; Copied from LSR #105 and renamed.
   ;; Included here to allow this module to provide a complete set of
   ;; common formal operations on motives, i.e transposition,
   ;; inversion and retrograding.
 
-  (let* ((elements (ly:music-property music 'elements))
-         (arts (ly:music-property music 'articulations))
-         (reversed (reverse elements))
-         (element (ly:music-property music 'element))
-         (span-dir (ly:music-property music 'span-direction)))
-
-    (ly:music-set-property! music 'elements reversed)
-
-    (for-each retrograde-music arts)
-
-    (if (ly:music? element)
-        (ly:music-set-property!
-         music 'element
-         (retrograde-music element)))
-
-    (if (ly:dir? span-dir)
-        (ly:music-set-property! music 'span-direction (- span-dir)))
-
-    (for-each retrograde-music reversed)
-
-    music))
+  (define (reverse-span! m)
+    ;; invert direction of two-sided spanners
+    (let ((spd (ly:music-property m 'span-direction)))
+      (if (ly:dir? spd)
+          (begin
+            (set! (ly:music-property m 'span-direction) (- spd))
+            (case (ly:music-property m 'name)
+              ((CrescendoEvent)
+               (make-music 'DecrescendoEvent m))
+              ((DecrescendoEvent)
+               (make-music 'CrescendoEvent m))
+              (else m)))
+          m)))
+
+  ;; carryover is a possible list of tie events, the loop returns any
+  ;; such trailing list from the given expression
+  (define (loop m carryover)
+    (define (filter-ties! m carryover field)
+      (let ((vals (ly:music-property m field)))
+        (if (pair? vals)
+            (call-with-values
+                (lambda ()
+                  (partition! (music-type-predicate
+                               '(tie-event glissando-event)) vals))
+              (lambda (ties no-ties)
+                (set! (ly:music-property m field)
+                      (append! (map! reverse-span! no-ties) carryover))
+                ties))
+            (begin
+              (if (pair? carryover)
+                  (set! (ly:music-property m field) carryover))
+              '()))))
+
+    ;; The reversal will let some prefatory material stay in front of
+    ;; the following element.  Most prominently single
+    ;; overrides/reverts/sets/unsets and applyContext.  This does not
+    ;; change the position of a clef (which will generally be useless
+    ;; after retrograding) but it does not jumble the clef change
+    ;; command internals.  Also, stuff like \once\override stays at
+    ;; the affected element.
+
+    (define (prefatory? m)
+      (or ((music-type-predicate
+            '(apply-context apply-output-event layout-instruction-event)) m)
+          (and
+           (music-is-of-type? m 'music-wrapper-music)
+           (prefatory? (ly:music-property m 'element)))))
+
+    (define (musiclistreverse lst)
+      (let loop ((lst lst) (res '()) (zeros '()))
+        (cond ((null? lst) (reverse! zeros res))
+              ((prefatory? (car lst))
+               (loop (cdr lst) res (cons (car lst) zeros)))
+              (else
+               (loop (cdr lst) (reverse! zeros (cons (car lst) res)) '())))))
+
+    (cond ((music-is-of-type? m 'event-chord)
+           (let* ((chord-ties
+                   (append!
+                    (filter-ties! m carryover 'elements)
+                    ;; articulations on an event-chord do not occur
+                    ;; "naturally" but are supported when user-generated
+                    ;; elsewhere, so we treat them properly
+                    (filter-ties! m '() 'articulations)))
+                  ;; in-chord ties are converted to per-chord ties.
+                  ;; This is less than optimal but pretty much the
+                  ;; best we can hope to achieve with this approach.
+                  (element-ties
+                   (append-map!
+                    (lambda (m) (filter-ties! m '() 'articulations))
+                    (ly:music-property m 'elements))))
+             (append! chord-ties element-ties)))
+
+          ((music-is-of-type? m 'rhythmic-event)
+           (filter-ties! m carryover 'articulations))
+
+          ;; The following is hardly correct but tieing inside of
+          ;; <<...>> is really beyond our pay grade.
+          ((music-is-of-type? m 'simultaneous-music)
+           (append-map! (lambda (m) (loop m (ly:music-deep-copy carryover)))
+                        (ly:music-property m 'elements)))
+          (else
+           (let ((elt (ly:music-property m 'element))
+                 (elts (ly:music-property m 'elements)))
+             (let ((res
+                    (fold loop
+                          (if (ly:music? elt) (loop elt carryover) carryover)
+                          elts)))
+               (if (ly:music? elt)
+                   (set! (ly:music-property m 'element)
+                         (reverse-span! elt)))
+               (if (pair? elts)
+                   (set! (ly:music-property m 'elements)
+                         (map! reverse-span! (musiclistreverse elts))))
+               (append! res (filter-ties! m '() 'articulations)))))))
+  (let ((dangling (loop music '())))
+    (for-each
+     (lambda (t) (ly:music-warning t (_ "Dangling tie in \\retrograde")))
+     dangling))
+  music)
 
 (define-public (pitch-invert around to music)
   "If @var{music} is a single pitch, inverts it about @var{around}