Subdiv.Surf Modifier: whole or part of the object ?

On above BlenderGuru tutorial Andrew Price constructs the sink using Modifier: inner part of the sink becomes affected by the MOD. while outer/upper edges remain straight&ortho - still its the same object…??
How to deform part(s) of the object with the MODIFIER ?

The modifier affects the whole object, there is no way around this.
You can control its visual effect on your mesh with additional edge loops or applying a crease value (Shift+E) to an edge

Look at 9:52 in the vid.
You can see the rounded corner on the upper edge. Through most of the construction he is working with the sink object below the hole he cut in the counter. He also put a crease in the top edge of the sink bowl and that will also help to limit the deformation that gets passed along to the top edges.

It’s kind of tough to catch just what’s happening when someone works that quick.

Aaa-thats the missing catch !
The sink stays underneath the top practically…, I didnt see this, moreover-there were no screencast keys then to catch such momentary combination :-)…
Afaik CREASE cannot bring the edge back to straight 100% ??
Also-when I try LOOP-CUT & CREASE too close to the edge (the upper one here) it disappers => no space left for possible fillet value ?

Anyway-thank you, thats what i must have missed !