Declaration kinds

Every declaration starts with its kind: LootTable gems { ... } or ItemTag gems = [...]. There are 94 of them.

MMS kinds

These are MMS's own, for functions, text and other things the game has no single file for.

KindDoes
FunctionA function: commands, variables and control flow, compiled to .mcfunction files.
GlobalA value for the whole pack, set when the pack first loads.
JigsawHoleA name for jigsaw blocks, used only by the editor: JigsawHole road_end lists <namespace>:road_end in the Jigsaw view's Name and Target lists, so pieces built in the game join by names spelled the same way. It writes no file.
NamespaceSets the namespace for the declarations after it in the file.
ObjectiveA scoreboard objective, created by the generated load function.
OnAdvancementCode that runs as and at a player each time they meet a trigger: OnAdvancement name = Trigger(...) { ... } writes the advancement, its reward function and the revoke.
OnFirstJoinCode that runs once for each player, the first time they are in the world with the pack, as and at that player.
OnLoadCode that runs when the pack loads, from #minecraft:load.
OnRespawnCode that runs as and at a player right after they respawn.
OnTickCode that runs every tick, from #minecraft:tick.
StorageA record kept in command storage: Storage game: GameState keeps a Type GameState { wave: int = 0 } at <namespace>:mms game. Functions read and write its fields as game.wave; the pack sets each missing field to its default when it loads.
TestA test of the pack's functions, run by mms test and the editor: a setup { } block, then run f() and expect condition lines. Tests run in a fresh world after the pack loads and are never written to the pack.

Blueprint kinds

These are written in MMS, in the prelude. Each one writes several resources from one declaration, and has a page of its own.

KindDoes
BookA written book with pages in book markup: Book guide { title = "Guide", author = "The Garrison", text = ["# Welcome", "Plant the **banner** on gold."] }. Its name stands for the book in item stacks, loot entries and ${...} in commands.
CustomItemA vanilla item with its own look and name. It writes the model drawn from its texture, the item model that its item_model component names and its name in the lang files. Its name then stands for the base item with those components wherever an item stack goes: recipe results, loot entries and ${...} in commands.
JigsawStructureA structure grown from jigsaw pieces, with how often it appears: JigsawStructure dungeon { biomes = #minecraft:is_overworld, step = underground_structures, spacing = 32, separation = 12, height = AboveBottom(20), start = start, pools = { start = [Piece("start")] } }. It writes the structure set, the structure and one template pool per entry of pools. Its name stands for the structure, as in /locate structure ${dungeon}.

Resource kinds

Each of these makes one resource in the folder shown: in the data pack, or for assets/ folders in the resource pack. Tags of other registries follow the same pattern, such as DamageTypeTag.

KindFolder
Advancementdata/<namespace>/advancement/
Atlasassets/<namespace>/atlases/
BannerPatterndata/<namespace>/banner_pattern/
Biomedata/<namespace>/worldgen/biome/
BiomeTagdata/<namespace>/tags/worldgen/biome/
A tag of worldgen/biome entries. Other tags of the same registry follow Tag the same way.
BlockStateassets/<namespace>/blockstates/
BlockStateProviderdata/<namespace>/worldgen/block_state_provider/
BlockTagdata/<namespace>/tags/block/
A tag of block entries. Other tags of the same registry follow Tag the same way.
BlockTransformerdata/<namespace>/block_transformer/
Carverdata/<namespace>/worldgen/carver/
CatSoundVariantdata/<namespace>/cat_sound_variant/
CatVariantdata/<namespace>/cat_variant/
ChatTypedata/<namespace>/chat_type/
ChickenSoundVariantdata/<namespace>/chicken_sound_variant/
ChickenVariantdata/<namespace>/chicken_variant/
ContextFloatProviderdata/<namespace>/context_float_provider/
ContextIntProviderdata/<namespace>/context_int_provider/
CowSoundVariantdata/<namespace>/cow_sound_variant/
CowVariantdata/<namespace>/cow_variant/
DamageTypedata/<namespace>/damage_type/
DamageTypeTagdata/<namespace>/tags/damage_type/
A tag of damage_type entries. Other tags of the same registry follow Tag the same way.
DecoratedPotPatterndata/<namespace>/decorated_pot_pattern/
DensityFunctiondata/<namespace>/worldgen/density_function/
Dialogdata/<namespace>/dialog/
Dimensiondata/<namespace>/dimension/
DimensionTypedata/<namespace>/dimension_type/
Enchantmentdata/<namespace>/enchantment/
EnchantmentProviderdata/<namespace>/enchantment_provider/
EntityTypeTagdata/<namespace>/tags/entity_type/
A tag of entity_type entries. Other tags of the same registry follow Tag the same way.
Equipmentassets/<namespace>/equipment/
Featuredata/<namespace>/worldgen/feature/
FlatLevelGeneratorPresetdata/<namespace>/worldgen/flat_level_generator_preset/
FluidTagdata/<namespace>/tags/fluid/
A tag of fluid entries. Other tags of the same registry follow Tag the same way.
Fontassets/<namespace>/font/
FrogVariantdata/<namespace>/frog_variant/
FunctionTagdata/<namespace>/tags/function/
A tag of function entries. Other tags of the same registry follow Tag the same way.
Instrumentdata/<namespace>/instrument/
ItemModelassets/<namespace>/items/
ItemModifierdata/<namespace>/item_modifier/
ItemTagdata/<namespace>/tags/item/
A tag of item entries. Other tags of the same registry follow Tag the same way.
JukeboxSongdata/<namespace>/jukebox_song/
Langassets/<namespace>/lang/
LootTabledata/<namespace>/loot_table/
MaterialConditiondata/<namespace>/worldgen/material_condition/
MaterialRuledata/<namespace>/worldgen/material_rule/
Modelassets/<namespace>/models/
MultiNoiseBiomeSourceParameterListdata/<namespace>/worldgen/multi_noise_biome_source_parameter_list/
Noisedata/<namespace>/worldgen/noise/
NoiseSettingsdata/<namespace>/worldgen/noise_settings/
PaintingVariantdata/<namespace>/painting_variant/
Particleassets/<namespace>/particles/
PigSoundVariantdata/<namespace>/pig_sound_variant/
PigVariantdata/<namespace>/pig_variant/
PlacedFeaturedata/<namespace>/worldgen/placed_feature/
PostEffectassets/<namespace>/post_effect/
Predicatedata/<namespace>/predicate/
ProcessorListdata/<namespace>/worldgen/processor_list/
Recipedata/<namespace>/recipe/
SlotSourcedata/<namespace>/slot_source/
Structuredata/<namespace>/worldgen/structure/
StructureSetdata/<namespace>/worldgen/structure_set/
SulfurCubeArchetypedata/<namespace>/sulfur_cube_archetype/
SurfaceConditiondata/<namespace>/worldgen/material_condition/
SurfaceRuledata/<namespace>/worldgen/material_rule/
TemplatePooldata/<namespace>/worldgen/template_pool/
TestEnvironmentdata/<namespace>/test_environment/
TestInstancedata/<namespace>/test_instance/
Timelinedata/<namespace>/timeline/
TradeSetdata/<namespace>/trade_set/
TrialSpawnerdata/<namespace>/trial_spawner/
TrimMaterialdata/<namespace>/trim_material/
TrimPatterndata/<namespace>/trim_pattern/
VillagerTradedata/<namespace>/villager_trade/
WaypointStyleassets/<namespace>/waypoint_style/
WolfSoundVariantdata/<namespace>/wolf_sound_variant/
WolfVariantdata/<namespace>/wolf_variant/
WorldClockdata/<namespace>/world_clock/
WorldPresetdata/<namespace>/worldgen/world_preset/
ZombieNautilusVariantdata/<namespace>/zombie_nautilus_variant/