"your review bookmarks only for this chapter"

Sol, at the upper right of the posting view you now show whether or not I've reviewed someone's chapter, and whether it was inline or regular. Immediately to the left of that, right below the stack of coins, is a little icon that looks like a message. When I hover over it, the tooltip says "your review bookmarks only for this chapter".

What is that for/does it mean?

Thanks.
Dirk