What a kind means
A component kind identifies an interface concept: action.button, overlay.dialog, navigation.tabs or input.combobox. It says what the pattern means and how it behaves. It does not choose a component library.
The initial registry describes anatomy, states, keyboard interaction, accessibility and motion. The registry is extensible because no fixed list can describe every domain-specific interface.
Anatomy makes composition explicit
A dialog can contain a backdrop, surface, title, description, content, actions and close control. A combobox can contain an input, trigger, popup, listbox and options. Named slots preserve those relationships when the visual arrangement changes.
Anatomy is more useful than a pile of rectangles: it explains which item labels another, which trigger controls a surface, and which region becomes scrollable.
Definitions and instances
A component definition declares a reusable contract. An instance refers to that definition and supplies instance content, properties or permitted overrides. Several instances share the definition without sharing runtime state unless explicitly modeled.
A component family can expose variants such as primary, secondary and destructive. The visual difference does not remove the underlying action semantics.
Similar appearance does not imply equivalent behavior
A modal dialog, non-modal popover and context menu can share a surface style while having different focus, keyboard and dismissal requirements. Classify the pattern by behavior first. Map it to an existing design-system primitive only after checking that the contracts agree.
Platform examples in the registry describe possible mappings. The project does not claim that those platform adapters are implemented or that same-named widgets are always equivalent.