code: def is_subdomain(domain, reference):
      
      index_of_reference = domain.find(reference)
      if index_of_reference > 0 and domain[index_of_reference:] == reference:
          return True
      return False
docs: Tests if a hostname is a subdomain of a reference hostname
      e.g. www.domain.com is subdomain of reference
  
      @param domain: Domain to test if it is a subdomain
      @param reference: Reference "parent" domain