Group causes reflow because when it's appended it puts relay element with connectedCallback that fires once connected, which triggers new appends and replacement of this relay.
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It's not entirely clear if this is a problem indeed, but one of the solution could be appending elements directly to DocumentFragment when group is not connected, so that it can connect nodes without relay.
Groupcauses reflow because when it's appended it putsrelayelement withconnectedCallbackthat fires once connected, which triggers new appends and replacement of thisrelay.⬇️
It's not entirely clear if this is a problem indeed, but one of the solution could be appending elements directly to
DocumentFragmentwhengroupis not connected, so that it can connect nodes withoutrelay.