The NATS client libraries can take a full URL, nats://demo.nats.io:4222, to specify a specific server host and port to connect to.
Libraries are removing the requirement for an explicit protocol and may allow nats://demo.nats.io:4222 or just demo.nats.io:4222. Check with your specific client library's documentation to see what URL formats are supported.
For example, to connect to the demo server with a URL you can use:
!INCLUDE "../../_examples/connect_url.html"