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# NSIsControllerMarker(_:)

Tests whether a given object is special marker object used for indicating the state of a selection in relation to a key.

```
func NSIsControllerMarker(_ object: Any?) -> Bool
```

## Parameters

`object`

Specify the object you want to check. This parameter can be `nil`.

## Return Value

<doc://com.apple.documentation/documentation/Swift/true> if the object is one of the designated controller markers or <doc://com.apple.documentation/documentation/Swift/false> if it is not.

## Discussion

This function helps you to create bindings between user interface elements and controller objects. The Application Kit predefines several special marker objects used as values for indicating selection state; currently these are [`NSMultipleValuesMarker`](/documentation/AppKit/NSMultipleValuesMarker), [`NSNoSelectionMarker`](/documentation/AppKit/NSNoSelectionMarker), and [`NSNotApplicableMarker`](/documentation/AppKit/NSNotApplicableMarker). These markers are typed as `id` and only exist for the purpose of indicating a state; they are never archived and cannot be used as object values in controls. You use this function to test whether a given object value is a marker, in which case it is not directly assignable to the object that is bound. This check is important, especially since additional markers may be added in the future.

See the `NSKeyValueBinding.h` header file for further details.

---

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