+\version "2.19.29"
+
+"\\=" =
+#(define-event-function (id event) (number-or-string? 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
+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))
+ event)