Layout

Custom GUIs use a Layout-To-Char system where each character corresponds to a slot in the inventory. To function correctly, the number of slots must match the inventory's type and size.

Examples:

Chest:

- "         "
- "         " # 3*9 = 27 slots/size
- "         "

Dropper:

- "   "
- "   " # 3*3 = 9 slots/size
- "   "

Double-Chest:

- "         "
- "         "
- "         "
- "         " # 9*6 = 54 slots/size
- "         "
- "         "

You can then replace one space with a character (a-z, 0-9) and edit it through the elements section. Take a look at the Element documentation