Purpose of referrer
referrer supplies the URL context used to resolve src.
A relative src is resolved against that URL, while a module-path
src uses it to select the matching import-map scope. An absolute
src remains unchanged.
The referrer may itself be a relative URL, module path, or absolute URL.
It changes URL resolution only; it does not enter another component's local
module-map context. Use referrer-selector when resolution must use
the context owned by a rendered descendant component.