Function detect_level 

pub fn detect_level() -> Level

The instruction set the vectorized encoder paths run on.

Detected at runtime where the platform allows it (std builds, wasm), otherwise the best level this crate was compiled for. The std answer is cached: probing costs a dozen feature tests, and callers such as crate::enc::bit_cost::BrotliPopulationCost dispatch once per histogram, deep inside the clustering loops.