Package swaggerui serves Swagger UI, embedded in the binary, for the
openapi package:
openapi.New(openapi.Options{UI: swaggerui.New()})
Importing it adds about 1.5 MB to the binary, which is why it is a package of
its own: an app that only wants the document does not import it. Nothing is
fetched from the network, so the page works offline and under a strict
Content-Security-Policy that allows same-origin scripts and styles (Swagger
UI sets inline styles, so style-src needs 'unsafe-inline').
Routes returns the routes that serve the page under base (a path ending in
"/", such as "/docs/") for the document at specPath. The openapi package
calls it.