Merge attr and props

[dy]

attr use-cases are limited - reflecting something in DOM, like, in markup. That is needed for hydration, selecting something via CSS (styling from outside). There's almost no sense deserializing internal component props - they should be always real props, not some fake attributes.

Note: not all attributes are reflected to props: aria-, dataset (not necessarily), itemset, class, style, data-* attributes etc. Ideally these are handled by appropriate domains.

One possible solution - fall back to incremental-dom way: primitives are reflected to attrs, fns and objects are not.

The other possible (svelte) solution - detect which props are defined on elements as props and reflect them as attrs, otherwise use props.

Considering #48 as well - what strategy is the most favorable for K.?

[dy]

. <div attr="..." /> is a meta-effect, similar to <div children="..." />

[dy]

See #48. Different domains are actually more useful. If elements internally map props to atts and vv - not framework concern.