ReadonlybufferReadonlyinstanceInstances that made it into the tree (hidden and non-invertible ones do not).
ReadonlymaxLevels of nodes on the longest top-level path.
ReadonlynodeReadonlyrecordtraceableIndex order: recordOrder[recordIndex] is the position in the input array.
ReadonlyskippedInstances left out because their transform cannot be inverted.
Header, records and nodes in one buffer, ready for
writeBuffer.