Simple question about set...

Question

Does it only trigger when there is an assignment to the property or does it trigger with any change further on down the line? Like, if I have a property named MyProp in MyClass of type TestClass (assume testclass has a TestField field), will MyProp trigger the set code with a line like "MyProp.TestField = "cows are pretty"" or would it only trigger on something like "MyProp = MyOtherTestClass"