Parameter locks
In a normal step sequencer a step says one thing: play the note. A parameter lock lets the step also say how: this hat a little more closed, this kick from a different sample, this snare through a longer reverb.
The lock lives on the step. When the sequencer reaches it, the parameter jumps to the locked value; when it reaches a step without that lock, the parameter goes back to the track's own setting. Nothing is drawn as automation, so the pattern stays one short loop that you can still change while it plays.
Locks are what turn a four-bar loop into a part that breathes: accents, a slice that changes every other bar, a delay throw on one beat.
