Macro dom_renderer 

macro_rules! dom_renderer {
    ($register:path, $backend:ty, kind: $kind:expr, props: $props:ty, patch: $patch:ty,
     make: $make:expr, update: $update:expr, measure: $measure:expr $(,)?) => { ... };
    ($register:path, $backend:ty, kind: $kind:expr, props: $props:ty, patch: $patch:ty,
     make: $make:expr, update: $update:expr $(,)?) => { ... };
    ($register:path, $backend:ty, kind: $kind:expr, props: $props:ty,
     make: $make:expr, measure: $measure:expr $(,)?) => { ... };
    ($register:path, $backend:ty, kind: $kind:expr, props: $props:ty, make: $make:expr $(,)?) => { ... };
}

Register a piece’s web-dom renderer, whose registry is populated at RUNTIME.

linkme has no wasm32-unknown-unknown implementation (DESIGN.md §8.2), so day-dom keeps a Registry<Dom> that pieces add to by calling day_dom::register_renderer. This macro is renderer!’s counterpart for that seam: same typed make/update/measure, same inserted downcast, but it defines an idempotent pub(crate) fn register() instead of a static — and the piece’s own constructor must call it, which is the one line web pieces write that link-time ones don’t:

// lib-dom.rs
day_pieces::dom_renderer!(day_dom::register_renderer, day_dom::Dom,
    kind: KIND, props: MyProps, patch: MyPatch, make: make, update: update, measure: measure);

// lib.rs — a constructor always runs before the node it returns is realized.
pub fn my_piece(…) -> MyPiece {
    #[cfg(all(feature = "dom", target_arch = "wasm32"))]
    dom_impl::register();
    …
}

One dom_renderer! per module.