HELP ABOUT SLUR OFFSET

[MX]

Hi all, bonjour à tous.

1. How can I ajust the position of the beginning of the slur in the 
picture attached ?

I tried to override the control-points property of the slur object but I 
couldn't find rules to use it and I just want to push sligtly the 
beginning of the slur, not the entire slur. The property Slur 
#'attachment-offsets seemed to do that easyly but it does not exist 
anymore in the 2.6.0 release.

2. How can adjust the figure 3 in the tuplet ?

3. In a general manner, it's rather difficult to find in the doc what 
are all the properties for a given object and how to use them. Does 
exist anywhere in the doc a thesaurus of all the objects, and for each 
object all corresponding properties ?

Thank u in advance.

\version "2.6.1"
\include "italiano.ly"

pd = \change Staff = dessus
pb = \change Staff = basse

\header {
  title = "Extrait"
  subtitle = ""
  subsubtitle =""
}

dessus = \relative do {
  \times 2/3 {\stemUp \pb \once\override Slur #'attachment-offset = #'(100 . 2) 
mi8 ([ \pd do' \pb sol \pd mi' do\pb  sol ]) }
  \times 2/3 {\stemUp \pb mi8 ([ \pd do' \pb sol \pd mi' do\pb  sol ]) }
}

basse = \relative do, {
  \clef bass
  %1
  <do sol' do>1
}

\score {
  <<

    \context PianoStaff <<
      \context Staff = "dessus" \dessus
      \context Staff = "basse" \basse
    >>
  >>
  \layout { 
    \context { }
  }
  \midi { \tempo 4 = 112 }
}