I have attached 2 cropped screen-captures of the same class displayed in the class browser;
class-smalltalk.png is the regular class syntax,
class-fluid.png is the same class but with the "Fluid" checkbox selected, and shows a different syntax.

May I know what that is all about?

There's a different terminology too, something called "slot", which I have faint memories of being quite like that in "Self" environments.

Thank you,

~Kathe