app basics and doc structure

docs/examples/app/event01.py

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+from textual.app import App
+from textual import events
+
+
+class EventApp(App):
+
+    COLORS = [
+        "white",
+        "maroon",
+        "red",
+        "purple",
+        "fuchsia",
+        "olive",
+        "yellow",
+        "navy",
+        "teal",
+        "aqua",
+    ]
+
+    def on_mount(self) -> None:
+        self.styles.background = "darkblue"
+
+    def on_key(self, event: events.Key) -> None:
+        if event.key.isdecimal():
+            self.styles.background = self.COLORS[int(event.key)]
+
+
+app = EventApp()
+if __name__ == "__main__":
+    app.run()

docs/examples/app/return.py

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+from textual.app import App, ComposeResult
+from textual.widgets import Button
+
+
+class ButtonsApp(App):
+    def compose(self) -> ComposeResult:
+        yield Button("Paul")
+        yield Button("Duncan")
+        yield Button("Chani")
+
+
+app = ButtonsApp()
+if __name__ == "__main__":
+    app.run()

docs/examples/app/simple01.py

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+from textual.app import App
+
+
+class MyApp(App):
+    pass

docs/examples/app/simple02.py

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+from textual.app import App
+
+
+class MyApp(App):
+    pass
+
+
+app = MyApp()
+if __name__ == "__main__":
+    app.run()

docs/examples/app/widgets01.py

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+from textual.app import App, ComposeResult
+from textual.widgets import Welcome
+
+
+class WelcomeApp(App):
+    def compose(self) -> ComposeResult:
+        yield Welcome()
+
+    def on_button_pressed(self) -> None:
+        self.exit()
+
+
+app = WelcomeApp()
+if __name__ == "__main__":
+    app.run()