Okay, that answers what it is I saw ... it was prototyping. I'd never seen it before and couldn't find any reference documentation for it because I didn't know what it was called. Thanks. :-)
Note: My initial example contained a colon (:) in the prototype when really it should have been a semi-colon (;)
I can recommend Tom Christiansens' rant against prototyping on why in general you want to stay away from it, even though the article is about 5 years old now.