In Rhinoceros and Grasshopper a surface is a simple geometry "Represents a base class that is common to most RhinoCommon surface types. A surface represents an entity that can be all visited by providing two independent parameters, usually called (u, v), or sometimes (s, t)."
In UV space it is a rectangle !! https://wiki.mcneel.com/rhino/nurbssurfaces
I have already opened all files from Pufferfish V3.0 Examples, but I didn’t find something like that. A few scripts didn’t work with my Mac, unfortunately.
All of Pufferfish works fine with Mac. Tween doesn’t work with solid trimmed geometry like those letters. Make them mesh with equal topology. The structure in question uses the batwing component from mesh+ as the morphing unit along twisted boxes.