As the title says:

Advancements, loot tables, resource pack names and world folder names do not require to be lower cased, unlike models, structures, textures, etc.

There are even advancements that have upper/camel case in the name (e.g., the folder buildingBlocks) and wolds are called New World(for single player) and World(for multiplayer) by default.

Expected behavior: all files need to be lower cased like within resource packs.

Files that allow uppercase:

• advancements
• loot tables
• world folders