Tree Structure
Simple explanation
A Tree is the parsed result you keep: it owns its text and all its nodes, tells you its root, whether anything is broken, and can diff itself against another tree.
Technical explanation
tree/tree.zig owns source (a copy of the parsed bytes), the SubtreePool, and root_index. Operations: rootNode() (handle, no allocation), hasError() (reads the root flag), copy() (deep duplicate with the tree's allocator), includedRange(), languageOf(), sourceText(), plus the allocator-inheriting cursor(), getChangedRanges(), and freeChangedRanges(). Trees are immutable after parsing except for applyEdit, which shifts stored positions through an edit's translation.