Coolant tank on Volvo M11

[deerfeeder]

I've got a 99 Volvo with an M11. Had to replace a pipe off the bottom of water pump. The pipe had a slow leak, and got low enough to shut the engine down once. Luckily it was parked. Filled the right side, checked it and added some till I got a chance to change the pipe. The plastic tank on top of the radiator has a right and left side. The cap on the right side says coolant, left one only has waves like water. I'm sure these are both for coolant, but why two parts to the tank ? I filled the right side when it shut down. Is the left side an overflow ? Should I only add anti-freeze and water to the right side ?
Can anyone tell the total coolant capacity ?

[deerfeeder]

Well, I called a Volvo shop today, and I'm smarter than I was. The left side IS the overflow tank. Not where anti-freeze should be added.