We have automatic chaining, so you don't need to use "from X" unless you want to have some control on the traceback message. Even without knowing of this syntax (and without using "from exc"), a user will get a traceback message similar to what is shown in the example. What is the purpose of the entire section then?

As I see it, the purpose might be providing some details about how exactly chaining works, so a user: a) could make an informed decision whether they need "from X" or not, b) would know how to retrieve the linked exception programmatically.

I generally feel that we don't want to deprive a user from special attributes, in Python they are everywhere, you cannot even construct a class instance without __init__().