docs: add explanation about stream wrapper

Author: kenjis

user_guide_src/source/testing/overview.rst

@@ -285,14 +285,24 @@ Testing CLI Input
 **PhpStreamWrapper** provides a way to write tests for methods that require user input,
 such as ``CLI::prompt()``, ``CLI::wait()``, and ``CLI::input()``.
 
+.. note:: The PhpStreamWrapper is a stream wrapper class.
+    If you don't know PHP's stream wrapper,
+    see `The streamWrapper class <https://www.php.net/manual/en/class.streamwrapper.php>`_
+    in the PHP maual.
+
 **Overview of methods**
 
-- ``PhpStreamWrapper::register()`` Register the ``PhpStreamWrapper`` to php protocol.
+- ``PhpStreamWrapper::register()`` Register the ``PhpStreamWrapper`` to the ``php`` protocol.
 - ``PhpStreamWrapper::restore()`` Restore the php protocol wrapper back to the PHP built-in wrapper.
 - ``PhpStreamWrapper::setContent()`` Set the input data.
 
+.. important:: The PhpStreamWrapper is intended for only testing ``php://stdin``.
+    But when you register it, it handles all the `php protocol <https://www.php.net/manual/en/wrappers.php.php>`_
+    such as ``php://stdout``, ``php://stderr``, ``php://memory``.
+    So it is strongly recommended that ``PhpStreamWrapper`` be registered/unregistered
+    only when needed. Otherwise, it will interfere with other built-in php streams
+    while registered.
+
 An example demonstrating this inside one of your test cases:
 
 .. literalinclude:: overview/019.php
-
-.. note:: It is strongly recommended that ``PhpStreamWrapper`` be registered/unregistered only when needed. Otherwise, it will interfere with other built-in php streams while registered.