Question about DMG Reduc..

Does the % to Reduce X damage from shields stack with regular damage reduction? I know say the ring of mastery reduc does not stack with the Shroud reduc for example, but because its a % chance to reduce I'm wondering if it would. Or at the very least say if its % to reduce 200 Damage and always 50 damage, would the 50 DMG stick on the times that the % to reduce doesn't, then when the % goes off it takes precedence over the straight up reduction?

If theyre both 100% chance to block they will not stack at all. If its a damage % it stacks almost the exact same way that stone and poison does. So lets say you got Shroud first and shield second (item order matters) Your shroud will block 100% of the time however when ever shield blocks it will overide shrouds block.

How Poison stacks with Stone or Purge
Any time Stone or Purge proc poison will not be in that attack this goes unnoticed as poison last like 8 seconds. Before any ask dont worry poison stacks with lifesteal from the Primarchs Scepter 100%. All lifesteal attacks will be laced with poisoned attacks.