where is "t" defined in the cadquery-cycloidal example? (noob question)

[ht55ght55]

I'm trying to understand the logic and I probably can't see something obvious. Please help!

[sgenoud]

The t is just an argument of the cycloidal functions (I am using arrow functions).

The value of the parameter t is then filled by the sketchParametricFunction, at different points to create an interpolation.