While reading your post for the first time I got the impression that you were looking for data type "Natural" \-- I searches for Natural in docs and found it fast. But now I have the impression that you are looking for keyword "type"?
Keyword type is mentioned in tutorial 1, maybe not early enough. Well, explaining something can be difficult if one does not know the audience. The "type" keyword and the type section is in no way an invention of Nim, Pascal, Modula, Oberon have it. Generally, when we explain something, we have to start somewhere. Whenever I read a science paper, there are a dozen of new terms for me, often I have to consult other papers to learn their meaning. But of course Nim devs will continue to improve docs.
