Comment by rabarbers

Thanks for explaining! But how about this example:

  x:42
  {x+1}[5]

It results in

  6

It seems like you can define variables with the name 'x', but when you do not have explicit parameters, then the identifier 'x' is used to refer to the first implicit parameter, y - for second and z - for the third parameter. In context of implicit parameters x, y and z acts like predefined keywords.