[webkit-dev] Could someone explain a bit on document fragments?

I see, for a large page, that a document is created and then a number of fragments. Are these fragments all then merged into that document? Or are they merged into one another, forming a new document somehow? Where is that done? What would be a acceptable way to measure the total time spent parsing? Going from parser creation to parser finish doesn't work when there are many document fragments, each with it's own parser. Should I add up the time spent in all of the parsers? Thanks, --Murph