QIODevice base function return values are not documented

The documentation for QIODevice is at:

https://doc.qt.io/qt-5/qiodevice.html

https://doc.qt.io/qt-6.2/qiodevice.html

https://doc.qt.io/qt-6/qiodevice.html

The return values of the base implementations of the various virtual functions are undocumented, which presents a fair amount of uncertainty when implementing QIODevice-derived classes.

For example, QIODevice::isSequential currently reads:

Returns true if this device is sequential; otherwise returns false.

Sequential devices, as opposed to a random-access devices, have no concept of a start, an end, a size, or a current position, and they do not support seeking. You can only read from the device when it reports that data is available. The most common example of a sequential device is a network socket. On Unix, special files such as /dev/zero and fifo pipes are sequential.

Regular files, on the other hand, do support random access. They have both a size and a current position, and they also support seeking backwards and forwards in the data stream. Regular files are non-sequential.

Leaving one to wonder whether or not they should reimplement it for [non-]sequential QIODevices. 

Notes similar to "the base implementation returns false" (or maybe it's true; not sure) could be added to the existing documentation.

The other functions documented there are similar.

There may be other classes in the documentation with similar issues. I find it to be particularly important for QIODevice, whose subclasses must exhibit very specific behaviors and invariants in order to function correctly.

As a consequence, the only safe way to currently implement a QIODevice-subclass is to either implement every virtual function with a non-void return – which seems to counter the intent of the API (minimizing number of overrides needed) – or to dig into the Qt source to find the return values, both of which add a lot of potentially unnecessary work (= higher risk for mistakes).