<%= yield %> <%# Vendored libs above don't change between deploys, so they're left unversioned; app.js's own modules do, and map.js statically imports them by bare path — an import map remaps those paths to a versioned URL so editing e.g. gpx.js also busts its cache, without having to touch every file's import statements. Must come before the module script below: the importmap has to be parsed first. %>