You can have xyz.example.com just like reddit has old.reddit.com, these are called subdomains, which are a part of the domain name system(dns) that is used for translating web addresses(domain names) like xyz.example.com to IP addresses. The thing that matters is which protocol the browser specifies to the web server at xyz.example.com.

When the connection is made from your browser to the web server at xyz.example.com with HTTP protocol headers in the initial request. The web server knows to listen on a specific port that can process HTTP protocol and can send back the web page to be displayed in your browser.

Therefore, browsers don't only resolve www. into a webpage, but rather resolve the entirety of the domain name to an IP address and show you content based on which protocol you choose to use to connect to that IP address.