It also represents a stable API and ABI, both in the kernel... https://illumos.org/man/9F/avl https://illumos.org/man/9F/avl ... and in user mode, via libavl:

It also represents a stable API and ABI, both in the kernel... https://illumos.org/man/9F/avl https://illumos.org/man/9F/avl ... and in user mode, via libavl: https://illumos.org/man/3LIB/libavl https://illumos.org/man/3LIB/libavl Our debugger, MDB, is able to use the offsets and pointers stored in the tree to provide generic walks through any AVL tree in a live system, core file, or crash dump.