More specifically: the first unknown identifier becomes the first parameter for the closest algorithm defined with {} brackets. Properties (also called named algorithms) are defined as {} context. And KatLang program also is defined as {} context. I call it Second order algorithm - algorithms can contain another algorithms. First order algorithm is something defined between commas or semicolons. But inside brackets () or {} you can define second order algorithm.

You might like looking at how Dyalog handles higher-order functions; John Scholes really put this beautiful presentation together about using them as a depth-first search reusable function https://www.youtube.com/watch?v=DsZdfnlh_d0 and if you haven't seen it, you should!