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docs/reference/out-of-bounds.md

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+# out of bounds
+
+The behavior of functions whose parameter values are out of bounds.
+
+Many of the BBC micro:bit functions have parameters. If a parameter is an unexpected value, the parameter is considered *out of bounds*.
+
+For example, the [plot](/microbit/reference/led/plot) function has two parameters:
+
+### syntax
+
+```
+export function plot(x: number, y: number)
+```
+
+### parameters
+
+* x - the *x coordinate* or horizontal position (0, 1, 2, 3, 4)
+* y - the *y coordinate* or vertical position (0, 1, 2, 3, 4)
+
+### out of bounds
+
+here's an example of code with an out of bounds parameter (the *x* and *y* parameters are outside the expected range of 0-4):
+
+```
+led.plot(9, -21)
+```
+
+### what happens?
+
+Typically, when a parameter supplied to a function is out of bounds that function does nothing (as if the function never executed). So, in the above case, the LED screen will not change.
+
+### return value
+
+If you call the `point` function with an out of bounds parameter, the function returns `false`:
+
+```
+let on = led.point(5, -5)
+```
+
+### see also
+
+For more information on the out-of-bounds behavior of a function, see the documentation for that [function](/microbit/js/contents).
+