performLayout method
Implementation
@override
void performLayout(ChantContext ctxt) {
super.performLayout(ctxt);
build(ctxt)
..withPodatus(lower: notes[0], upper: notes[1])
..advanceBy(ctxt.intraNeumeSpacing * 0.68)
..withInclinata(notes.sublist(2));
finishLayout(ctxt);
}