Detecting Mana?

Is there a way to detect how much mana a unit has? I want to be able to drain a unit's mana and add however much it had to the amount of lumber the player has. I have a unit casting siphon mana on units when they get close, but I want it to target the units with the most mana first, or at least not target units below, say, 25% of their mana. Is there a way to do that? Thanks

If you want to get the mana of a unit:
"Real - unit - property of unit"
"Real - unit - percentage mana"

If you want to modify the mana of a unit:
"Action - unit - set mana - to value"
"Action - unit - set mana - to percentage"