Controllers are plain JavaScript objects that manage interaction state — which item is focused, what is selected, whether groups are expanded. They have no DOM dependency and can be tested without a browser.

Available controllers

ListController — flat and grouped list navigation with single/multi-select; supports nested tree navigation when used with the navigator action
NestedController — tree navigation with expand/collapse
TabularController — row/column navigation for data tables

ListController

Manages a flat or grouped list. Items are identified by a value field. Supports single selection (default), multi-selection, and type-ahead search.

Method	Description
`setItems(items, fields)`	Load items with field mapping
`focusNext()`	Move focus to next item
`focusPrev()`	Move focus to previous item
`focusFirst()`	Move focus to first item
`focusLast()`	Move focus to last item
`select(value)`	Select item by value
`search(char)`	Type-ahead: jump to matching item

NestedController

Extends ListController for hierarchical data. Tracks expanded/collapsed state per group using path keys. Follows WAI-ARIA TreeView keyboard patterns.

Method	Description
`expand(path)`	Expand group; if already expanded, move focus to first child
`collapse(path)`	Collapse group; if on a child, move focus to parent
`toggle(path)`	Toggle expand/collapse state

See @rokkit/states for full API reference and usage examples.