The tier boundary

Components live under packages/react/src/components/<tier>/ — atoms, molecules, or organisms. The boundary is a rule you can apply mechanically, not a judgment call, and it decides where a component lives and what it's allowed to do.

The rule

Ask these questions in order:

1. Does it render into a portal, trap focus, or manage open/closed state across multiple sub-elements? It's an organism — Dialog, Select, Combobox, DropdownMenu.
2. Is it assembled from two or more atoms with no such orchestration? It's a molecule — Card, Alert, FormField, Pagination.
3. Otherwise it's an atom — single-purpose, not further divisible: Button, Input, Badge, Separator.

Why the line sits there

The boundary tracks behavioral complexity, not visual size. Overlay orchestration — portals, focus management, keyboard navigation across children — is where accessibility bugs live, so the components that do it are quarantined in one tier where the shared interaction hooks and heavier test suites apply. A molecule stays simple enough to review at a glance; the moment it grows open/closed state across sub-elements, it's an organism and moves.

Edge cases, decided

• SegmentedControl manages a selected value and arrow-key navigation, but across sibling radio options with no portal or open/closed state — molecule.
• Accordion manages expanded state across multiple items — organism, even though it renders no portal.
• NavigationMenu renders an always-visible nested list — every item with an href is a real link (an item without one is an inert group label), no disclosure state. It's an organism for its compound structure, but note it deliberately has no open/close behavior.
• FormField wires ids and ARIA attributes to an arbitrary child — wiring, not orchestration — molecule.

What the tier changes in practice

• The import path: @elirobinson/react/components/<tier>/<Name> — moving a component between tiers is a breaking change.
• Review depth: organisms require keyboard-contract tests; their component pages must document focus behavior precisely.
• Composition direction: organisms may compose molecules and atoms; molecules compose atoms; atoms compose nothing from the system.