code: Rule assignmentExpression() {
  		return Sequence(
  				assignmentLHS(), set(),
  				assignmentOperator().label("operator"),
  				group.basics.optWS(),
  				assignmentExpressionChaining().label("RHS"),
  				set(actions.createAssignmentExpression(value(), text("operator"), lastValue())));
  	}
docs: TODO add checks to see if an LHS that isn't valid for assignment shows up as a syntax error of some sort, e.g. a.b() = 2;