Style and Behavior are deliberately different

The package separates two concerns that ordinary component props often mix together.

Style is appearance as data. It can carry classes, inline declarations, recipes, themes, pseudo selectors, media queries and other deterministic CSS rules.

Behavior is reusable element-level interaction. Useful examples include:

tooltip wiring
analytics click tracking
ARIA decoration
keyboard behavior
focus management
ResizeObserver
intersection observer

A Behavior may contribute attributes and a Mount, but it does not own application state.

That boundary is important. If a behavior needs a widget's selected value, open state, request state or domain data to become its private mutable state, the right abstraction is still Foldkit: Model/Submodel + Message + update + Commands. Mixins should not become React hooks in Foldkit clothing.