I was always under impression that Sprint Backlog is part of Product Backlog -> it's impossible to add anything into Sprint Backlog without affecting Product Backlog
However, according to one of the comments to this postthis post, these backlogs "are completely different artifacts"
We are using an electronic Scrum board; would it be possible to add things like items from our Retrospective into Sprint backlog and avoid messing up Product backlog?