\version "2.19.23"

off =
#(define-music-function
  (spec event)
  (pair? ly:music?)
  "Shift grobs using X- and Y-offset, with outside-staff-priority unset by default.

Provides dedicated input modes for Dynamics in order to handle the tricky interaction with DynamicLineSpanner and both settings of outside-staff-priority.
"
  ;; default values
  (define x-off 0)
  (define y-off 0)
  (define inside-staff? #t)
  (define dynamic? #f)
  (define dyn-line-off 0)

  (define (spec-type? spec symbol-list)
    (and (list? spec)
         (member (car spec) symbol-list)))

  ;; Apply tweak only if cond? is true
  (define (cond-tweak cond? prop val arg)
    (if cond? (tweak prop val arg) arg))

  ;; differentiate between spec-types
  (cond
   ((number-pair? spec)
    (set! x-off (car spec))
    (set! y-off (cdr spec)))
   ;; Offset DynamicText and Hairpin.
   ((spec-type? spec '(dynamic dyn d))
    (set! dynamic? #t)
    (set! x-off (second spec))
    (set! y-off (third spec)))
   ;; Offset DynamicLineSpanner; Y-offset only
   ((spec-type? spec '(dynamic-line dyn-line dl))
    ;; Allow requiring outside-staff placement
    ;; by giving #f as an additional element.
    (if (= 3 (length spec)) (set! inside-staff? (third spec)))
    (set! dyn-line-off (second spec)))
   (else (ly:warning "Cannot read specification for offset - using default values.")))

  (cond-tweak inside-staff? 'outside-staff-priority #f
    (offset 'X-offset x-off
      (offset 'Y-offset y-off
        (cond-tweak
         (and dynamic? inside-staff?)
         '(DynamicLineSpanner outside-staff-priority)
         #f
         (offset '(DynamicLineSpanner Y-offset) dyn-line-off event))))))

\relative {
  \hideNotes
  \dynamicUp
  b'2-\off #'(dl 0) -\off #'(d 0 0) \< 2\f\>
  2 2\!\<
  2\f
}