An unordered Markdown list can be written as [YAML](markdown.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
             }
          ]
       }
    ]