Slurs can be made with complex dash patterns by defining
the dash-definition property. dash-definition
is a list of dash-elements. A dash-element is a
list of parameters defining the dash behavior for a segment of
the slur.
The slur is defined in terms of the bezier parameter t
which ranges from 0 at the left end of the slur to 1 at the right end of the slur.
dash-element is a list (start-t stop-t dash-fraction
dash-period). The region of the slur from start-t to
stop-t will have a fraction dash-fraction
of each dash-period black. dash-period is
defined in terms of staff spaces. dash-fraction is
set to 1 for a solid slur.