The topology of a polygon mesh object. You can modify a mesh topology by getting its Topology attribute, modifying the value using a topology node, and then setting the Topology attribute. Alternatively, you can replace an object's topology simply by setting a new Topology value.
Setting the Topology attribute is time-consuming because it essentially executes all the topology operations that have been accumulated so far. In particular, avoid setting it inside a loop like Repeat or While. A good strategy is to save the value as a custom attribute inside the loop, and then set the actual Topology attribute afterward.
Apart from intrinsic attributes like PointPosition and so on, the ICE attributes of new components are set to the default values. They are not interpolated in the same way that, for example, weights are interpolated when you add new points using non-ICE operators. This means that you can find new components by setting a custom attribute like PreExisting to True, setting Topology, and then filtering for PreExisting = False.
You can create invalid geometry like disconnected vertices. These vertices are automatically cleaned up after the entire tree is evaluated, but they still exist between execution branches of the tree. However, getting attributes on these invalid vertices will give incorrect values, even for intrinsic attributes like PointPosition.