Minecraft wiki entry for difficulty, associated text: Specifies the new difficulty level. Must be one of the following:
peaceful (can be abbreviated as p or 0‌[Bedrock Edition only]) for peaceful difficulty
easy (can be abbreviated as e or 1‌[Bedrock Edition only]) for easy difficulty
normal (can be abbreviated as n or 2‌[Bedrock Edition only]) for normal difficulty
hard (can be abbreviated as h or 3‌[Bedrock Edition only]) for hard difficulty
If unspecified, queries the current difficulty instead of changing it.‌[Java Edition only]