We might have a roll button like

value="[[@{str} + @{dex} + @{con} + @{int} + @{wiz} + @{cha}]]"

Are values like @{str} drawn from the character sheet, or from Roll20's servers?

If the latter, and you have a value like that with 6 attributes, does Roll20 bundle them up in a single class or is that six separate calls?

Finally is each inline roll [[ ]] a separate call to Roll20's servers?