At the beginning of https://docs.python.org/3.7/library/io.html#io.RawIOBase, we declared that 

> Binary I/O (also called buffered I/O)
and 
> Raw I/O (also called unbuffered I/O)

But we didn't mention if Text I/O use buffer or not which led to confusion. Even though we talked about it later in https://docs.python.org/3.7/library/io.html#class-hierarchy

> The TextIOBase ABC, another subclass of IOBase, deals with streams whose bytes represent text, and handles encoding and decoding to and from strings. TextIOWrapper, which extends it, is a buffered text interface to a buffered raw stream (BufferedIOBase). Finally, StringIO is an in-memory stream for text.

IMO, it will be better to declare 'Reads and writes are internally buffered in order to speed things up' at the very beginning in 

> Text I/O
> Text I/O expects and produces str objects...

or maybe

> class io.TextIOBase
> Base class for text streams. This class provides a character and line based interface to stream I/O. It inherits IOBase. There is no public constructor.

It's just an implementation detail.  Python implementation and C implementation behave slightly different.  But user program shouldn't rely on the detail.

Why do you think implementation details should be declared?
Who needs the information?

I found the document is not that clear when I try to understand what happens when Python read/write a file. I'm not sure who also needs this information. As you said, It wouldn't help the user program in Python. However, make it more clear maybe help users have a better feeling of what is happening under the hood.

I still think it's too detailed.
Reading C and Python code is much better way to understand such implementation detail.