An unordered Markdown list can be written as YAML, like this:

- object-group:
    - protocol:
        - tcp-udp: both TCP and UDP
    - port:
        - ssh: 22
        - https: 443
- port:
    - ftp-data: 20
    - ftp: 21
    - smtp: 25
    - domain: 53
    - www: 80

Why is this interesting? Because the text can be rendered as HTML. . .

• object-group:
  • protocol:
    • tcp-udp: both TCP and UDP
  • port:
    • ssh: 22
    • https: 443
• port:
  • ftp-data: 20
  • ftp: 21
  • smtp: 25
  • domain: 53
  • www: 80

. . . as well as being manipulated programmatically. You could convert it to JSON, for example:

[
   {
      "object-group" : [
         {
            "protocol" : [
               {
                  "tcp-udp" : "both TCP and UDP"
               }
            ]
         },
         {
            "port" : [
               {
                  "ssh" : 22
               },
               {
                  "https" : 443
               }
            ]
         }
      ]
   },
   {
      "port" : [
         {
            "ftp-data" : 20
         },
         {
            "ftp" : 21
         },
         {
            "smtp" : 25
         },
         {
            "domain" : 53
         },
         {
            "www" : 80
         }
      ]
   }
]