Understanding the regular expression /^\/node?(?:\/(\d+)(?:\.\.(\d+))?)?/

Understanding the regular expression /^\/node?(?:\/(\d+)(?:\.\.(\d+))?)?/

I can understand that / in the beginning and the end are regex delimiters,
also ^\/node is for a string starting with /node What's happening after
that beats me!
Any help would be great!