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+#Pinout Overlays
+
+A Pinout overlay describes the functions of the Raspberry Pi pins for a specific board.
+
+An overlay is constructed from a JSON file and, optionally, a markdown file containing an extended long-description.
+
+##JSON Format
+
+The JSON overlay file must include a name, manufacturer name, URL, description 
+( short description required, long is optional ) and a "pin" array.
+
+The pin array must list each pin by its *physical* location, and include at least a "name" describing the function
+of that pin.
+
+Optionally each pin definition can include an "exclusive" flag, which marks this pin as being unavailable for other
+use when it's occupied by this add-on.
+
+Things like i2c/SPI wont normally be flagged as exclusive, but most general purpose GPIO pins would, for example.
+
+Example:
+
+```json
+{
+	"name": "Pibrella",
+	"manufacturer": "Pimoroni",
+	"url": "https://github.com/pimoroni/pibrella",
+	"description": {
+		"short": "An all-in-one light, sound, input and output add-on board.",
+		"long": "pibrella.md"
+	},
+	"pin": {
+		"7": {
+			"name": "Green LED",
+			"exclusive": "true"
+		},
+		"11": {
+			"name": "Yellow LED",
+			"exclusive": "true"
+		}
+	}
+}
+```