Container

In the APG, the parent element that groups a set of related widgets or content and carries the role saying what the group is — the tablist holding tabs, the listbox holding options, the menu holding items

The container is where the group's meaning lives, and getting it wrong is the common failure: tabs that are each a tab but sit in a plain <div> announce as unrelated buttons, because nothing said they were a set. Ownership has to be expressed too — either by nesting, or by aria-owns when the DOM cannot nest them — since assistive technology reads the tree, not the layout.

In the Agentic DS draft's kind enum, a component with an open composition slot and no state of its own — columns, a grid, a section

A passive layout. It adds nothing to the nesting-depth count, because it has no state to compound. Its slots still need statefulAllows, since something stateful could land in them. A pattern's group.container must be one. This is not the APG container: that is the role-bearing parent of a composite's items (a tablist holding tabs), which holds only its own kind of child. This one holds anything.

In CSS, an element that establishes a containment context, which is what @container queries measure against

Unrelated to the APG sense and worth not confusing: this one is a layout mechanism (container-type: inline-size) and carries no meaning for assistive technology at all. See container queries.