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Traversal

Traversal is the keyboard's answer to the pointer's targeting: four commands that move the selection through the tree without touching the mouse — down into children, up to parents, and across siblings. They are primitive commands (registry entries like any other); this document owns their semantics, and routing owns how the same keys resolve elsewhere (Enter inside a text session, Tab across widgets).

Down — Enter​

Enter binds the alternative chain enter-content-edit → select-children:

  1. Single editable leaf selected (text, vector): enter its content mode per the edit-mode dispatch table — the keyboard twin of the double-click descend-then-enter idiom (TGT-4). A leaf has no children, so the two meanings never compete on real trees; the chain order merely makes the tie impossible by construction.
  2. Otherwise: replace the selection with the union of the selected nodes' children. A childless, non-editable selection makes Enter a no-op — it never falls through to the host.

Repeated Enter walks the tree level by level: container → its children → their children — the keyboard equivalent of repeated double-clicks, except it fans out (all children) rather than following a pointer path.

Up — Shift+Enter​

Replace the selection with the union of the selected nodes' parents. Top-level nodes (children of the scene root) are already at the surface: they contribute themselves, and when the whole selection is top-level the command is a no-op — the scene root is never selected by traversal. Shift+Enter is the exact inverse walk of Enter's descent, and it also serves as the exit ramp from a deep click: dive with the deep modifier, then Shift+Enter back out level by level.

Across — Tab / Shift+Tab​

Tab replaces the selection with the next sibling of the traversal anchor — the most recently selected node — in document order; Shift+Tab the previous. The walk wraps at both ends, skips inactive nodes, and includes locked ones (traversal is a tree operation, not a canvas pick — HIER-6's split applies). A multi-node selection collapses to the anchor's neighbor: Tab is deliberately a single-selection instrument.

With an empty selection, Tab selects the scene's first top-level node — an entry point, so the keyboard can reach the tree from nothing.

Reveal — the camera follows​

Traversal must never select off-screen invisibly. When a traversal command's result is not fully inside the viewport, the camera pans the minimal distance to reveal it (no zoom change). This mirrors the hierarchy panel's reveal rule (HIER-4) on the canvas side: keyboard navigation always shows you what it just did.

Contracts​

  • TRAV-1 Enter on a container selection selects exactly the union of children, replacing the selection; on a single editable leaf it enters content-edit; on a childless non-editable selection it is a no-op.
  • TRAV-2 Shift+Enter selects the union of parents; on an all-top-level selection it changes nothing; the scene root is never selected.
  • TRAV-3 Enter then Shift+Enter from a single container round- trips to the original selection.
  • TRAV-4 Tab cycles siblings in document order with wrap-around; N siblings need exactly N Tabs to return; Shift+Tab reverses the cycle; inactive siblings are skipped, locked ones are not.
  • TRAV-5 Traversal is view-safe: after any traversal command, the selection's bounds intersect the viewport (the camera panned if needed), and no document mutation or history entry occurred.