diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9077cffff..dfe88fbc0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
-## [0.1.9] - Unreleased
+## [0.1.10] - Unreleased
+
+### Changed
+
+- Allowed callbacks to be async or non-async, and for event to be optional.
+- Fixed exception in clock example https://github.com/willmcgugan/textual/issues/52
+
+## [0.1.9] - 2021-08-06
 
 ### Added
 
diff --git a/README.md b/README.md
index 1595fcfdb..20af6c947 100644
--- a/README.md
+++ b/README.md
@@ -56,14 +56,14 @@ from textual.app import App
 
 
 class Beeper(App):
-    async def on_key(self, event):
+    def on_key(self):
         self.console.bell()
 
 
 Beeper.run()
 ```
 
-Here we can see a textual app with a single `on_key` method which will receive key events. Any key event will result in playing the terminal bell (which will generally emit an irritating beep). Hit Ctrl+C to exit.
+Here we can see a textual app with a single `on_key` method which will handle key events. Pressing any key will result in playing the terminal bell (generally an irritating beep). Hit Ctrl+C to exit.
 
 Event handlers in Textual are defined by convention, not by inheritance (so you won't find an `on_key` method in the base class). Each event has a `name` attribute which for the key event is simply `"key"`. Textual will call the method named `on_<event.name>` if it exists.
 
@@ -74,7 +74,7 @@ from textual.app import App
 
 
 class ColorChanger(App):
-    async def on_key(self, event):
+    def on_key(self, event):
         if event.key.isdigit():
             self.background = f"on color({event.key})"
 
@@ -82,7 +82,9 @@ class ColorChanger(App):
 ColorChanger.run(log="textual.log")
 ```
 
-This example also handles key events, and will set `App.background` if the key is a digit. So pressing the keys 0 to 9 will change the background color to the corresponding [ansi color](https://rich.readthedocs.io/en/latest/appendix/colors.html).
+You'll notice that the `on_key` method above contains an additional `event` parameter which wasn't present on the beeper example. If the `event` argument is present, Textual will call the handler with an event object. Every event has an associated handler object, in this case it is a KeyEvent which contains additional information regarding which key was pressed.
+
+The key event handler above will set the background attribute if you press the keys 0-9, which turns the terminal to the corresponding [ansi color](https://rich.readthedocs.io/en/latest/appendix/colors.html).
 
 Note that we didn't need to explicitly refresh the screen or draw anything. Setting the `background` attribute to a [Rich style](https://rich.readthedocs.io/en/latest/style.html) is enough for Textual to update the visuals. This is an example of _reactivity_ in Textual. To make changes to the terminal interface you modify the _state_ and let Textual update the UI.
 
@@ -90,17 +92,16 @@ Note that we didn't need to explicitly refresh the screen or draw anything. Sett
 
 To make more interesting apps you will need to make use of _widgets_, which are independent user interface elements. Textual comes with a (growing) library of widgets, but you can develop your own.
 
-Let's look at an app which contains widgets. We will be using the built in `Placeholder` widget which you can use to design application layouts before you implement the real content.
+Let's look at an app which contains widgets. We will be using the built-in `Placeholder` widget which you can use to design application layouts before you implement the real content.
 
 ```python
-from textual import events
 from textual.app import App
 from textual.widgets import Placeholder
 
 
 class SimpleApp(App):
 
-    async def on_mount(self, event: events.Mount) -> None:
+    async def on_mount(self) -> None:
         await self.view.dock(Placeholder(), edge="left", size=40)
         await self.view.dock(Placeholder(), Placeholder(), edge="top")
 
@@ -108,7 +109,9 @@ class SimpleApp(App):
 SimpleApp.run(log="textual.log")
 ```
 
-This app contains a single event handler `on_mount`. The mount event is sent when the app or widget is ready to start processing events, and is typically used for initialization. In this case we are going to call `self.view.dock` to add widgets to the interface.
+This app contains a single event handler `on_mount`. The mount event is sent when the app or widget is ready to start processing events, and is typically used for initialization. You may have noticed that `on_mount` is an `async` function. Since Textual is an asynchronous framework we will need this if we need to call most other methods.
+
+The `on_mount` method makes two calls to `self.view.dock` which adds widgets to tht terminal.
 
 Here's the first line in the mount handler:
 
@@ -145,7 +148,6 @@ Let's look at an example with a custom widget:
 ```python
 from rich.panel import Panel
 
-from textual import events
 from textual.app import App
 from textual.reactive import Reactive
 from textual.widget import Widget
@@ -153,22 +155,22 @@ from textual.widget import Widget
 
 class Hover(Widget):
 
-    mouse_over: Reactive[bool] = Reactive(False)
+    mouse_over = Reactive(False)
 
     def render(self) -> Panel:
         return Panel("Hello [b]World[/b]", style=("on red" if self.mouse_over else ""))
 
-    async def on_enter(self, event: events.Enter) -> None:
+    def on_enter(self) -> None:
         self.mouse_over = True
 
-    async def on_leave(self, event: events.Leave) -> None:
+    def on_leave(self) -> None:
         self.mouse_over = False
 
 
 class HoverApp(App):
-    """Hover widget demonstration."""
+    """Demonstrates custom widgets"""
 
-    async def on_mount(self, event: events.Mount) -> None:
+    async def on_mount(self) -> None:
         hovers = (Hover() for _ in range(10))
         await self.view.dock(*hovers, edge="top")
 
@@ -179,26 +181,34 @@ HoverApp.run(log="textual.log")
 The `Hover` class is a custom widget which displays a panel containing the classic text "Hello World". The first line in the Hover class may seem a little mysterious at this point:
 
 ```python
-mouse_over: Reactive[bool] = Reactive(False)
+mouse_over = Reactive(False)
 ```
 
-This adds a `mouse_over` attribute to your class which is a bool with a default of `False`. The typing part (`Reactive[bool]`) is not required, but will help you find bugs if you are using a tool like [Mypy](https://mypy.readthedocs.io/en/stable/). Adding attributes like this makes them _reactive_, and any changes will result in the widget updating.
+This adds a `mouse_over` attribute to your class which is a bool with a default of `False`. Adding attributes like this makes them _reactive_: any changes will result in the widget updating.
 
-The following `render()` method is where you define how the widget should be displayed. In the Hover widget we return a Panel containing rich text with a background that changes depending on the value of `mouse_over`. The goal here is to add a mouse hover effect to the widget, which we can achieve by handling two events: `Enter` and `Leave`. These events are sent when the mouse enters or leaves the widget.
+The following `render()` method is where you define how the widget should be displayed. In the Hover widget we return a [Panel](https://rich.readthedocs.io/en/latest/panel.html) containing rich text with a background that changes depending on the value of `mouse_over`. The goal here is to add a mouse hover effect to the widget, which we can achieve by handling two events: `Enter` and `Leave`. These events are sent when the mouse enters or leaves the widget.
 
 Here are the two event handlers again:
 
 ```python
-    async def on_enter(self, event: events.Enter) -> None:
+    def on_enter(self) -> None:
         self.mouse_over = True
 
-    async def on_leave(self, event: events.Leave) -> None:
+    def on_leave(self) -> None:
         self.mouse_over = False
 ```
 
 Both event handlers set the `mouse_over` attribute which, because it is reactive, will result in the widget's `render()` method being called.
 
-The app class has a `Mount` handler where we _dock_ 10 of these custom widgets from the top edge, stacking them vertically. If you run this script you will see something like the following:
+The `HoverApp` has a `on_mount` handler which creates 10 Hover widgets and docks them on the top edge, creating a vertical stack.
+
+```python
+    async def on_mount(self) -> None:
+        hovers = (Hover() for _ in range(10))
+        await self.view.dock(*hovers, edge="top")
+```
+
+If you run this script you will see something like the following:
 
 ![widgets](./imgs/custom.gif)
 
diff --git a/docs/examples/actions/colorizer.py b/docs/examples/actions/colorizer.py
index 8ba59cfa6..4034f7a8d 100644
--- a/docs/examples/actions/colorizer.py
+++ b/docs/examples/actions/colorizer.py
@@ -2,7 +2,7 @@ from textual.app import App
 
 
 class Colorizer(App):
-    async def on_load(self, event):
+    async def on_load(self):
         await self.bind("r", "color('red')")
         await self.bind("g", "color('green')")
         await self.bind("b", "color('blue')")
diff --git a/docs/examples/actions/q.py b/docs/examples/actions/q.py
deleted file mode 100644
index 682be8591..000000000
--- a/docs/examples/actions/q.py
+++ /dev/null
@@ -1,9 +0,0 @@
-from textual.app import App
-
-
-class Quiter(App):
-    async def on_load(self, event):
-        await self.bind("q", "quit")
-
-
-Quiter.run()
diff --git a/docs/examples/messages_and_events/beep.py b/docs/examples/messages_and_events/beep.py
index 6dfa99a6a..7cbd54de0 100644
--- a/docs/examples/messages_and_events/beep.py
+++ b/docs/examples/messages_and_events/beep.py
@@ -2,7 +2,7 @@ from textual.app import App
 
 
 class Beeper(App):
-    async def on_key(self, event):
+    def on_key(self):
         self.console.bell()
 
 
diff --git a/docs/examples/messages_and_events/color_changer.py b/docs/examples/messages_and_events/color_changer.py
index 8507b2336..7d43a65e7 100644
--- a/docs/examples/messages_and_events/color_changer.py
+++ b/docs/examples/messages_and_events/color_changer.py
@@ -2,7 +2,7 @@ from textual.app import App
 
 
 class ColorChanger(App):
-    async def on_key(self, event):
+    def on_key(self, event):
         if event.key.isdigit():
             self.background = f"on color({event.key})"
 
diff --git a/docs/examples/widgets/custom.py b/docs/examples/widgets/custom.py
index 7be00ed8a..6856bcb20 100644
--- a/docs/examples/widgets/custom.py
+++ b/docs/examples/widgets/custom.py
@@ -1,4 +1,3 @@
-from rich.console import RenderableType
 from rich.panel import Panel
 
 from textual.app import App
@@ -10,7 +9,7 @@ class Hover(Widget):
 
     mouse_over = Reactive(False)
 
-    def render(self) -> RenderableType:
+    def render(self) -> Panel:
         return Panel("Hello [b]World[/b]", style=("on red" if self.mouse_over else ""))
 
     def on_enter(self) -> None:
diff --git a/src/textual/geometry.py b/src/textual/geometry.py
index 7743890c6..ef540dae2 100644
--- a/src/textual/geometry.py
+++ b/src/textual/geometry.py
@@ -125,7 +125,7 @@ class Size(NamedTuple):
                 "Dimensions.__contains__ requires an iterable of two integers"
             )
         width, height = self
-        return bool(width > x >= 0 and height > y >= 0)
+        return width > x >= 0 and height > y >= 0
 
 
 class Region(NamedTuple):
@@ -164,7 +164,7 @@ class Region(NamedTuple):
         """
         x, y = origin
         width, height = size
-        return Region(x, y, width, height)
+        return cls(x, y, width, height)
 
     def __bool__(self) -> bool:
         return bool(self.width and self.height)
@@ -182,7 +182,7 @@ class Region(NamedTuple):
         return self.x + self.width
 
     @property
-    def y_end(self) -> int:
+    def y_max(self) -> int:
         return self.y + self.height
 
     @property
@@ -216,7 +216,7 @@ class Region(NamedTuple):
 
     @property
     def y_range(self) -> range:
-        return range(self.y, self.y_end)
+        return range(self.y, self.y_max)
 
     def __add__(self, other: Any) -> Region:
         if isinstance(other, tuple):
diff --git a/src/textual/layout.py b/src/textual/layout.py
index f74647ada..610e39e4f 100644
--- a/src/textual/layout.py
+++ b/src/textual/layout.py
@@ -307,7 +307,7 @@ class Layout(ABC):
         height = self.height
         screen = Region(0, 0, width, height)
 
-        crop_region = crop or Region(0, 0, self.width, self.height)
+        crop_region = crop.intersection(screen) if crop else screen
 
         _Segment = Segment
         divide = _Segment.divide
@@ -326,23 +326,15 @@ class Layout(ABC):
         # Go through all the renders in reverse order and fill buckets with no render
         renders = list(self._get_renders(console))
 
-        clip_y, clip_y2 = crop_region.y_extents
         for region, clip, lines in chain(
             renders, [(screen, screen, background_render)]
         ):
-            # clip = clip.intersection(crop_region)
             render_region = region.intersection(clip)
-            for y, line in enumerate(lines, render_region.y):
-                if clip_y > y > clip_y2:
-                    continue
-                # first_cut = clamp(render_region.x, clip_x, clip_x2)
-                # last_cut = clamp(render_region.x + render_region.width, clip_x, clip_x2)
-                first_cut = render_region.x
-                last_cut = render_region.x_max
-                final_cuts = [cut for cut in cuts[y] if (last_cut >= cut >= first_cut)]
-                # final_cuts = cuts[y]
+            for y, line in zip(render_region.y_range, lines):
+
+                first_cut, last_cut = render_region.x_extents
+                final_cuts = [cut for cut in cuts[y] if (last_cut >= cut >= first_cut)]
 
-                # log(final_cuts, render_region.x_extents)
                 if len(final_cuts) == 2:
                     cut_segments = [line]
                 else: