Macro web_main 

macro_rules! web_main {
    ($root:expr) => { ... };
    ($title:expr, $root:expr) => { ... };
}

Expands to the day_dom_main C export the web host’s shim.js calls once the wasm module is instantiated (wasm.day_dom_main() at the end of start() in crates/day-cli/resources/web/shim.js).

day::web_main!(root);              // or: day::web_main!("My App", root);