Grace notes and beaming
If two grace notes are at exactly the same position (the same tick), they are put onto the same stem, as a chord. If multiple grace notes in front of the same note are put on different positions (even if they are only one tick apart), they are grouped under a beam.
It is possible to have beamed grace notes overlapping a beam of regular notes, as in the example below:
Grace notes in the middle of a group of regular notes