Insert a group block inside a list item

My solution is to use CSS to simulate numbers (or bullets) on a group (which is a <div>). So I first created groups within groups, and then I added CSS class on the topmost group:

.numbered-list {
    counter-reset: item;
}

And for each item, the group has this class:

.numbered-list-item {
}
.numbered-list-item:before {
    content: counter(item) "";
    counter-increment: item;
    line-height: 1;
    display: block;
}

Now the groups behave just like a numbered list, and they can contain anything.