doc: add note about reset_ouput_buffer and USB devices
diff --git a/documentation/pyserial_api.rst b/documentation/pyserial_api.rst
index b038f91..6e9cf20 100644
--- a/documentation/pyserial_api.rst
+++ b/documentation/pyserial_api.rst
@@ -196,6 +196,9 @@
Clear output buffer, aborting the current output and
discarding all that is in the buffer.
+ Note, for some USB serial adapters, this may only flush the buffer of
+ the OS and not all the data that may be present in the USB part.
+
.. versionchanged:: 3.0 renamed from ``flushOutput()``
.. method:: send_break(duration=0.25)