A Weighted Item Stack is like a normal IItemStack but has a percentage added to it.
You normally use them when dealing with percentage based actions like drops or secondary outputs.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.item.WeightedItemStack;

WeightedItemStack implements IWeightedIngredient. That means all functions available to IWeightedIngredient also are available to WeightedItemStack.

You can derive a weightedItemStack from an IItemStack by either using the modulo operator or the weight function on it.

ZenScript
 Copy
val itemStack = <minecraft:dirt>;

//both create a weightedItemstack object with a chance of 20%
val wItemStack = itemStack % 20;
val wItemStack2 = itemStack.weight(0.2);

ZenGetter	What does it do	Return Type
ZenGetter stack	What does it do Returns the associated itemStack	Return Type IItemStack
ZenGetter chance	What does it do Returns the stack's chance as decimal (e.g. 0.2)	Return Type float
ZenGetter percent	What does it do Returns the stack's chance as percentage (e.g. 20.0)	Return Type float