What is the extra 0 that shows up for attack and damage rolls whenever you use the monster character sheet from the compendium? EX: I click "Bite" for giant rat and it will roll me a "21 | 8". Hovering over the text it shows that I rolled a "1d20 + (4+0) = (17) + (4+0)" . What are the 0's referencing? Why are they there? What is the character sheet (5th edition (OGL by role 20)) doing that it computes the dice roll this way?