From 2ee61f95dbf57b4bbe7c7af29826ffd22be6632e Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Thu, 23 Feb 2023 14:37:47 +0000
Subject: [PATCH] Docs

---
 docs/guide/events.md        | 28 +++++++++++++++++++++++++++-
 src/textual/message_pump.py |  4 ++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/docs/guide/events.md b/docs/guide/events.md
index 7c3df74c4..3a6da3dae 100644
--- a/docs/guide/events.md
+++ b/docs/guide/events.md
@@ -108,7 +108,7 @@ The message class is defined within the widget class itself. This is not strictl
 - It creates a namespace for the handler. So rather than `on_selected`, the handler name becomes `on_color_button_selected`. This makes it less likely that your chosen name will clash with another message.
 
 
-## Sending events
+## Sending messages
 
 In the previous example we used [post_message()][textual.message_pump.MessagePump.post_message] to send an event to its parent. We could also have used [post_message_no_wait()][textual.message_pump.MessagePump.post_message_no_wait] for non async code. Sending messages in this way allows you to write custom widgets without needing to know in what context they will be used.
 
@@ -118,6 +118,32 @@ There are other ways of sending (posting) messages, which you may need to use le
 - [post_message_no_wait][textual.message_pump.MessagePump.post_message_no_wait] The non-async version of `post_message`.
 
 
+## Preventing messages
+
+You can *temporarily* prevent a Widget or App from posting messages or events of a particular type by calling [prevent][textual.message_pump.MessagePump.prevent], which returns a context manager. This is typically used when updating data in a child widget and you don't want to receive notifications that something has changed.
+
+The following example will play the terminal bell as you type, by handling the [Input.Changed][textual.widgets.Input.Changed] event. There's also a button to clear the input by setting `input.value` to empty string. We don't want to play the bell when the button is clicked so we wrap setting the attribute with a call to [prevent][textual.message_pump.MessagePump.prevent].
+
+!!! tip
+
+    In reality, playing the terminal bell as you type would be very irritating -- we don't recommend it!
+
+=== "prevent.py"
+
+    ```python title="prevent.py"
+    --8<-- "docs/examples/events/prevent.py"
+    ```
+
+    1. Clear the input without sending an Input.Changed event.
+    2. Plays the terminal sound when typing.
+
+=== "Output"
+
+    ```{.textual path="docs/examples/events/prevent.py"}
+    ```
+
+
+
 ## Message handlers
 
 Most of the logic in a Textual app will be written in message handlers. Let's explore handlers in more detail.
diff --git a/src/textual/message_pump.py b/src/textual/message_pump.py
index 061743722..bea707a02 100644
--- a/src/textual/message_pump.py
+++ b/src/textual/message_pump.py
@@ -546,11 +546,11 @@ class MessagePump(metaclass=MessagePumpMeta):
         """A context manager to *temporarily* prevent the given message types from being posted.
 
         Example:
-
+            ```python
             input = self.query_one(Input)
             with self.prevent(Input.Changed):
                 input.value = "foo"
-
+            ```
 
         """
         if self._prevent_events: