-- layout/header.wo — the header fragment (header.html's analog).
pub fn header() -> Text {
  let h = "<header class='site-header'>";
  h = h .. "<a href='/' class='brand'>writeonce shop</a>";
  h = h .. "<nav class='site-nav'><a href='/'>Products</a> <a href='/orders'>Orders</a></nav>";
  h = h .. "</header>";
  return h;
}