this is not exactly great, but it should be "good enough"
note that the new `group` function should not escape in the wild, as
we don't document it and only use it internally
I tried using `$[scale foo bar]` instead of `$[group foo bar]`, but
that would be rendered as `<i>foo bar</i>` when sent over the network
to non-misskey instances, and we don't want that
01a5300be8