ModAPI.keygen contains the API for getting item and block IDs from a string. It looks at the registries for items and blocks to derive the IDs, so IDs will not be automatically reserved until a block/item is actually registered. Ideally, you’d want to call a keygen method just before registering your block.
Methods:
ModAPI.keygen.item(itemId: String) : number
var id = ModAPI.keygen.item("my_example_item");ModAPI.keygen.block(blockId: String) : number
var id = ModAPI.keygen.block("my_example_block");