Closes #23

README.md

@@ -241,7 +241,26 @@ has no metadata payload. The payload types are:
 - `FrameInfo`
 - `SignalInfo`
 
-The tree supports browsing through the optional `DbcTreeModel` adapter.
+The tree is independent of Qt and supports browsing through the optional
+`DbcTreeModel` adapter. `GetParent()` returns a non-owning parent pointer;
+`GetRow()` returns the zero-based sibling position (zero for a detached node or
+root). `GetChild()` returns nullptr outside the child range, and `AddChild()`
+ignores null children. Appending children preserves existing addresses and rows.
+
+Nodes cannot be copied or moved. Transfer their `std::unique_ptr` ownership to
+preserve parent links and addresses. `AddChild()` accepts an rvalue ownership
+handle and rejects self/ancestor insertion and already-attached children with
+`std::invalid_argument` before consuming ownership. There is no detach or
+reparent operation; callers must supply exclusive ownership.
+
+`GetFrameKey()` returns `std::optional<FrameKey>` for frame nodes and signals
+directly attached to a frame. `GetSignalKey()` returns `std::optional<SignalKey>`
+for those signals. Roots, detached signals, and signals without a frame parent
+have no key. Keys use normalized CAN ID plus standard/extended type, and signal
+keys also include the signal name. They match runtime definition keys, remain
+independent of row order and frame display names, and survive source-database
+changes or destruction. Renaming a signal changes its logical identity. Returned
+keys are values and may be retained after destroying the tree.
 
 It is **not** the primary runtime decode structure.