Since grace notes effectively take zero time, special notation is used
to place something relative to a grace note. The begintime can be
followed by a number of grace notes to "back up" from the beat.
The number is a negative number enclosed in parentheses.
This must occur before the
stepsize offset,
if any (which would be specified within square brackets).
For example:
1: c; [grace] 8d; []e; []f; 2.g; ital above 1: 2(-3)[+1] "cresc."; bar
