code: function expandVertically() {
  		var growWith = 0;
  		for (var i = 0; i < this.virtualGridMatrix.length; i++) {
  			if (this.virtualGridMatrix[i][0] !== 0) {
  				growWith++;
  			}
  		}
  		if (growWith > 0) {
  			this.addEmptyRows(growWith);
  		}
  	}
docs: Add empty rows at bottom of the virtual grid.