Struct libjxl :: jxl :: ModularOptions
struct ModularOptions
{ ... };
size_t group_dim

Used in both encode and decode:

Encode options:

jxl::Predictor predictor
std::vector<uint32_t> splitting_heuristics_properties
jxl::ModularOptions::TreeKind tree_kind
jxl::ModularOptions::TreeMode wp_tree_mode