Optionalanchorwhere the node is anchored, when it is
the block's current version (selects the point encoding for lines)
the unread tail of the block, preserved for round-tripping
the layer name
the block's minimum reader version
the node's crdt id
the header byte between the block length and the versions
Zero in every well-formed file seen, but preserved rather than assumed.
the block-type discriminant
whether the layer is visible
the
0x02tree node block — a group's metadata (layer name/visibility)