doc update: add description of alt:// URL handler
diff --git a/documentation/url_handlers.rst b/documentation/url_handlers.rst
index 9814f24..dad518c 100644
--- a/documentation/url_handlers.rst
+++ b/documentation/url_handlers.rst
@@ -186,6 +186,32 @@
.. versionadded:: 3.0
+``alt://``
+==========
+This handler allows to select alternate implementations of the native serial port.
+
+Currently only the Posix platform provides alternative implementations.
+
+``PosixPollSerial``
+ Poll based read implementation. Not all systems support poll properly.
+ However this one has better handling of errors, such as a device
+ disconnecting while it's in use (e.g. USB-serial unplugged).
+
+``VTIMESerial``
+ Implement timeout using ``VTIME``/``VMIN`` of tty device instead of using
+ ``select``. This means that inter character timeout and overall timeout
+ can not be used at the same time. Overall timeout is disabled when
+ inter-character timeout is used. The error handling is degraded.
+
+
+Examples::
+
+ alt:///dev/ttyUSB0?class=PosixPollSerial
+ alt:///dev/ttyUSB0?class=VTIMESerial
+
+.. versionadded:: 3.0
+
+
Examples
========
@@ -196,5 +222,6 @@
- ``loop://?logging=debug``
- ``hwgrep://0451:f432`` (USB VID:PID)
- ``spy://COM54?file=log.txt``
+- ``alt:///dev/ttyUSB0?class=PosixPollSerial``