e.g. in Kotlin, when a function with only one parameter is accepted, in it's
definition, the first parameter name can be omitted and instead it's named `it`
implicitly:
strings.filter { it.length == 5 }.sortedBy { it }.map { it.toUpperCase() }
So there it's even part of the core language. In Nim it's only a part of certain stdlib templates, but it shows that there are other places, where such implicit things are used. Also the `it` is part of the template's name(`mapIt`, `applyIt`, ...).
