2 questions concerning skips and dynamics

[Thomas Ruedas]

Hi,
I came back to my attempts with the staff-centered dynamics in a piano 
score, and while the example I was pointed to in an earlier thread 
essentially works, I am still confused about two issues which I don't 
understand from the docs either. A test example (v.2.6.3) is at the 
bottom.
- How do skips really work, especially in connection with a 
dynamics-only system? In normal staves with proper notes they used to 
work as I expected, but not in the dynamics-only staff. For instance, 
I found some example with an expression like  s\f , which is 
apparently necessary to make the \f work; but how "wide" is the s? In 
my test case, it seems to have neither width 0 nor the width of the 
last nonzero skip.
Or take the first expressions in the test case,
s\mf s4. \setTextCresc s\<
Does the first s have zero width here? And why do I have to put s4. to 
get the cresc. at the beginning of the next bar? Is the \mf assigned 
a width?
I also replaced the s by \skip where possible, but the results were 
the same. The intended result of the test case is:
mf at the beginning
cresc. from bar 2, 1st eighth to b.3, 3rd eighth
f at b.3, 3rd eighth
decresc. directly after it for a period of one quarter
- The other question: in my test case, I can adjust the vertical 
position of dynamics text like mf or f and of the hairpins, but the 
text-version cresc. is too low. How do I adjust that?
I hope someone can help me out of this confusion.
Thomas

\version "2.6.3"

i = \context Staff {
        \context Voice = "i"
        \voiceOne
\clef treble \time 2/4 \repeat unfold 5 { d'8 fis' e' cis' }
}

dynamics = {
s\mf s4. \setTextCresc s\< s2 s4\f s\> s4\!
}

iii = \context Staff {
        \context Voice = "iii"
        \voiceTwo
\clef bass \time 2/4 \repeat unfold 5 { d4 a }
}

     \score {
       \context PianoStaff <<
         \context Staff = "upper" << \i >>
         \context Dynamics = dynamics \dynamics
         \context Staff= "lower" << \iii >>
       >>
       \layout {
         \context {
           \type "Engraver_group_engraver"
           \name Dynamics
           \alias Voice % So that \cresc works, for example.
           \consists "Output_property_engraver"

           \override VerticalAxisGroup #'minimum-Y-extent = #'(-1 . 1)

           \consists "Script_engraver"
           \consists "Dynamic_engraver"
           \consists "Text_engraver"

           \override TextScript #'font-size = #2
           \override TextScript #'font-shape = #'italic
           \override DynamicText #'extra-offset = #'(0 . 2.5)
           \override Hairpin #'extra-offset = #'(0 . 1.5)

           \consists "Skip_event_swallow_translator"

           \consists "Axis_group_engraver"
         }
         \context {
           \PianoStaff
           \accepts Dynamics
           \override VerticalAlignment #'forced-distance = #7
         }
       }
     }

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