Maze level cells use + as the layer separator.
The token before the first + is the bottom row. A blank token means air, so + means an empty cell and +M0 means air on the bottom row with M0 sitting at the same elevation a floor would support. Legacy h hole tokens are read as blank air.
Examples:
.+#+G+#is floor, wall, gem, wall..+#+#+#+#+#is floor with five walls stacked above it..+#+++#+#is floor, one wall, two empty layers, then two walls.