Fingering spanner
Draw a straight or dashed line between two fingerings.
Syntax is
-\guide dashed? offset -f
If Boolean argument dashed? is set to #t, draw a dashed line. The target fingering number is given by f, the offset from f to the start fingering is offset, which is coordinate pair (the X-value of this pair is thus always negative).
This function should be only used after the complete music has been typeset. Any change in the formatting will make the X-offsets invalid.