These placeholders return a boolean (True / False).
%SLIME_CHUNK% | Tells you if you are in a Slime Chunk (True, False).
%UPPER_CASE_SLIME_CHUNK% | Tells you if you are in a Slime Chunk (TRUE, FALSE).
%LOWER_CASE_SLIME_CHUNK% | Tells you if you are in a Slime Chunk (true, false).