# TwoStepCaretMovement
class
This plugin enables the two-step caret (phantom) movement behavior for [registered attributes](#function-registerAttribute) on arrow right (`→`) and left (`←`) key press.
Thanks to this (phantom) caret movement the user is able to type before/after as well as at the beginning/end of an attribute.
**Note:** This plugin support right–to–left (Arabic, Hebrew, etc.) content by mirroring its behavior but for the sake of simplicity examples showcase only left–to–right use–cases.
#### Forward movement
##### "Entering" an attribute:
When this plugin is enabled and registered for the `a` attribute and the selection is right before it (at the attribute boundary), pressing the right arrow key will not move the selection but update its attributes accordingly:
* When enabled:
```xml
foo{}<$text a="true">bar
```
```
→
```
```xml
foo<$text a="true">{}bar
```
* When disabled:
```xml
foo{}<$text a="true">bar
```
```
→
```
```xml
foo<$text a="true">b{}ar
```
##### "Leaving" an attribute:
* When enabled:
```xml
<$text a="true">bar{}baz
```
```
→
```
```xml
<$text a="true">bar{}baz
```
* When disabled:
```xml
<$text a="true">bar{}baz
```
```
→
```
```xml
<$text a="true">barb{}az
```
#### Backward movement
* When enabled:
```xml
<$text a="true">bar{}baz
```
```
←
```
```xml
<$text a="true">bar{}baz
```
* When disabled:
```xml
<$text a="true">bar{}baz
```
```
←
```
```xml
<$text a="true">ba{}rb{}az
```
#### Multiple attributes
* When enabled and many attributes starts or ends at the same position:
```xml
<$text a="true" b="true">bar{}baz
```
```
←
```
```xml
<$text a="true" b="true">bar{}baz
```
* When enabled and one procedes another:
```xml
<$text a="true">bar<$text b="true">{}bar
```
```
←
```
```xml
<$text a="true">bar{}<$text b="true">bar
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L155)
## Properties
### `_isGravityOverridden: boolean` _(readonly)_
`true` when the gravity is overridden for the plugin.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L667)
### `editor: Editor` _(readonly)_
The editor instance.
Note that most editors implement the [`ui`](module_core_editor_editor-Editor.md#member-ui) property. However, editors with an external UI (i.e. Bootstrap-based) or a headless editor may not have this property or throw an error when accessing it.
Because of above, to make plugins more universal, it is recommended to split features into:
* The "editing" part that uses the [`Editor`](module_core_editor_editor-Editor.md) class without `ui` property.
* The "UI" part that uses the [`Editor`](module_core_editor_editor-Editor.md) class and accesses `ui` property.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L33)
### `isEnabled: boolean` _(readonly)_
Flag indicating whether a plugin is enabled or disabled. A disabled plugin will not transform text.
Plugin can be simply disabled like that:
```typescript
// Disable the plugin so that no toolbars are visible.
editor.plugins.get( 'TextTransformation' ).isEnabled = false;
```
You can also use [`forceDisabled`](#function-forceDisabled) method.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L51)
### `_isNextGravityRestorationSkipped: boolean` _(private)_
A flag indicating that the automatic gravity restoration should not happen upon the next gravity restoration. [event-change:range](module_engine_model_selection-ModelSelection.md#event-change:range) event.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L173)
### `_overrideUid: string | null` _(private)_
The current UID of the overridden gravity, as returned by [`overrideSelectionGravity`](module_engine_model_writer-ModelWriter.md#function-overrideSelectionGravity).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L165)
### `attributes: Set` _(private)_
A set of attributes to handle.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L159)
#### Static properties
### `isContextPlugin: false` _(readonly)_
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L144)
### `pluginName: 'TwoStepCaretMovement'` _(readonly)_
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L178)
### `isOfficialPlugin: true` _(internal)_
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L185)
### `isPremiumPlugin: boolean` _(internal)_
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L160)
## Methods
### `constructor( editor )`
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L192)
#### Parameters
* `editor: Editor`
### `bind( bindProperty1, bindProperty2 ) → ObservableDualBindChain` _(inherited)_
Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.
Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.
Consider two objects: a `button` and an associated `command` (both `Observable`).
A simple property binding could be as follows:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```
or even shorter:
```typescript
button.bind( 'isEnabled' ).to( command );
```
which works in the following way:
* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.
**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).
You can also "rename" the property in the binding by specifying the new name in the `to()` chain:
```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```
It is possible to bind more than one property at a time to shorten the code:
```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```
which corresponds to:
```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```
The binding can include more than one observable, combining multiple data sources in a custom callback:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```
Using a custom callback allows processing the value before passing it to the target property:
```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```
It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:
```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L996)
#### Type parameters
* * `K1`
* `K2`
#### Parameters
* `bindProperty1: K1`
Observable property that will be bound to other observable(s).
* `bindProperty2: K2`
Observable property that will be bound to other observable(s).
#### Returns
* `ObservableDualBindChain`
The bind chain with the `to()` and `toMany()` methods.
### `bind( bindProperties ) → ObservableMultiBindChain` _(inherited)_
Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.
Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.
Consider two objects: a `button` and an associated `command` (both `Observable`).
A simple property binding could be as follows:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```
or even shorter:
```typescript
button.bind( 'isEnabled' ).to( command );
```
which works in the following way:
* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.
**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).
You can also "rename" the property in the binding by specifying the new name in the `to()` chain:
```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```
It is possible to bind more than one property at a time to shorten the code:
```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```
which corresponds to:
```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```
The binding can include more than one observable, combining multiple data sources in a custom callback:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```
Using a custom callback allows processing the value before passing it to the target property:
```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```
It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:
```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1074)
#### Parameters
* `bindProperties: Array<'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute' | '_handleForwardMovement' | '_handleBackwardMovement'>`
Observable properties that will be bound to other observable(s).
#### Returns
* `ObservableMultiBindChain`
The bind chain with the `to()` and `toMany()` methods.
### `bind( bindProperty ) → ObservableSingleBindChain` _(inherited)_
Binds [observable properties](#function-set:KEY_VALUE) to other objects implementing the [`Observable`](module_utils_observablemixin-Observable.md) interface.
Read more in the [dedicated](../framework/deep-dive/observables.md#property-bindings) guide covering the topic of property bindings with some additional examples.
Consider two objects: a `button` and an associated `command` (both `Observable`).
A simple property binding could be as follows:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled' );
```
or even shorter:
```typescript
button.bind( 'isEnabled' ).to( command );
```
which works in the following way:
* `button.isEnabled` **instantly equals** `command.isEnabled`,
* whenever `command.isEnabled` changes, `button.isEnabled` will immediately reflect its value.
**Note**: To release the binding, use [`unbind`](module_utils_observablemixin-Observable.md#function-unbind).
You can also "rename" the property in the binding by specifying the new name in the `to()` chain:
```typescript
button.bind( 'isEnabled' ).to( command, 'isWorking' );
```
It is possible to bind more than one property at a time to shorten the code:
```typescript
button.bind( 'isEnabled', 'value' ).to( command );
```
which corresponds to:
```typescript
button.bind( 'isEnabled' ).to( command );
button.bind( 'value' ).to( command );
```
The binding can include more than one observable, combining multiple data sources in a custom callback:
```typescript
button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
```
Using a custom callback allows processing the value before passing it to the target property:
```typescript
button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
```
It is also possible to bind to the same property in an array of observables. To bind a `button` to multiple commands (also `Observables`) so that each and every one of them must be enabled for the button to become enabled, use the following code:
```typescript
button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L918)
#### Type parameters
* `K`
#### Parameters
* `bindProperty: K`
Observable property that will be bound to other observable(s).
#### Returns
* `ObservableSingleBindChain`
The bind chain with the `to()` and `toMany()` methods.
### `clearForceDisabled( id ) → void` _(inherited)_
Clears forced disable previously set through [`forceDisabled`](#function-forceDisabled). See [`forceDisabled`](#function-forceDisabled).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L125)
#### Parameters
* `id: string`
Unique identifier, equal to the one passed in [`forceDisabled`](#function-forceDisabled) call.
#### Returns
* `void`
### `decorate( methodName ) → void` _(inherited)_
Turns the given methods of this object into event-based ones. This means that the new method will fire an event (named after the method) and the original action will be plugged as a listener to that event.
Read more in the [dedicated](../framework/deep-dive/observables.md#decorating-object-methods) guide covering the topic of decorating methods with some additional examples.
Decorating the method does not change its behavior (it only adds an event), but it allows to modify it later on by listening to the method's event.
For example, to cancel the method execution the event can be [stopped](module_utils_eventinfo-EventInfo.md#member-stop):
```typescript
class Foo extends ObservableMixin() {
constructor() {
super();
this.decorate( 'method' );
}
method() {
console.log( 'called!' );
}
}
const foo = new Foo();
foo.on( 'method', ( evt ) => {
evt.stop();
}, { priority: 'high' } );
foo.method(); // Nothing is logged.
```
**Note**: The high [priority](module_utils_priorities-PriorityString.md) listener has been used to execute this particular callback before the one which calls the original method (which uses the "normal" priority).
It is also possible to change the returned value:
```typescript
foo.on( 'method', ( evt ) => {
evt.return = 'Foo!';
} );
foo.method(); // -> 'Foo'
```
Finally, it is possible to access and modify the arguments the method is called with:
```typescript
method( a, b ) {
console.log( `${ a }, ${ b }` );
}
// ...
foo.on( 'method', ( evt, args ) => {
args[ 0 ] = 3;
console.log( args[ 1 ] ); // -> 2
}, { priority: 'high' } );
foo.method( 1, 2 ); // -> '3, 2'
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1159)
#### Parameters
* `methodName: 'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute' | '_handleForwardMovement' | '_handleBackwardMovement'`
Name of the method to decorate.
#### Returns
* `void`
### `delegate( events ) → EmitterMixinDelegateChain` _(inherited)_
Delegates selected events to another [`Emitter`](module_utils_emittermixin-Emitter.md). For instance:
```typescript
emitterA.delegate( 'eventX' ).to( emitterB );
emitterA.delegate( 'eventX', 'eventY' ).to( emitterC );
```
then `eventX` is delegated (fired by) `emitterB` and `emitterC` along with `data`:
```typescript
emitterA.fire( 'eventX', data );
```
and `eventY` is delegated (fired by) `emitterC` along with `data`:
```typescript
emitterA.fire( 'eventY', data );
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L539)
#### Parameters
* `events: Array`
Event names that will be delegated to another emitter.
#### Returns
* `EmitterMixinDelegateChain`
### `destroy() → void` _(inherited)_
Destroys the plugin.
**Note:** This method is optional. A plugin instance does not need to have it defined.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L137)
#### Returns
* `void`
### `fire( eventOrInfo, args ) → GetEventInfo[ 'return' ]` _(inherited)_
Fires an event, executing all callbacks registered for it.
The first parameter passed to callbacks is an [`EventInfo`](module_utils_eventinfo-EventInfo.md) object, followed by the optional `args` provided in the `fire()` method call.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L512)
#### Type parameters
* `TEvent: extends BaseEvent`
The type describing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).
#### Parameters
* `eventOrInfo: GetNameOrEventInfo`
The name of the event or `EventInfo` object if event is delegated.
* `args: TEvent[ 'args' ]`
Additional arguments to be passed to the callbacks.
#### Returns
* `GetEventInfo[ 'return' ]`
By default the method returns `undefined`. However, the return value can be changed by listeners through modification of the [`evt.return`](module_utils_eventinfo-EventInfo.md#member-return)'s property (the event info is the first param of every callback).
### `forceDisabled( id ) → void` _(inherited)_
Disables the plugin.
Plugin may be disabled by multiple features or algorithms (at once). When disabling a plugin, unique id should be passed (e.g. feature name). The same identifier should be used when [enabling back](#function-clearForceDisabled) the plugin. The plugin becomes enabled only after all features [enabled it back](#function-clearForceDisabled).
Disabling and enabling a plugin:
```typescript
plugin.isEnabled; // -> true
plugin.forceDisabled( 'MyFeature' );
plugin.isEnabled; // -> false
plugin.clearForceDisabled( 'MyFeature' );
plugin.isEnabled; // -> true
```
Plugin disabled by multiple features:
```typescript
plugin.forceDisabled( 'MyFeature' );
plugin.forceDisabled( 'OtherFeature' );
plugin.clearForceDisabled( 'MyFeature' );
plugin.isEnabled; // -> false
plugin.clearForceDisabled( 'OtherFeature' );
plugin.isEnabled; // -> true
```
Multiple disabling with the same identifier is redundant:
```typescript
plugin.forceDisabled( 'MyFeature' );
plugin.forceDisabled( 'MyFeature' );
plugin.clearForceDisabled( 'MyFeature' );
plugin.isEnabled; // -> true
```
**Note:** some plugins or algorithms may have more complex logic when it comes to enabling or disabling certain plugins, so the plugin might be still disabled after [`clearForceDisabled`](#function-clearForceDisabled) was used.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L111)
#### Parameters
* `id: string`
Unique identifier for disabling. Use the same id when [enabling back](#function-clearForceDisabled) the plugin.
#### Returns
* `void`
### `init() → void`
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L202)
#### Returns
* `void`
### `listenTo( emitter, event, callback, options? ) → void` _(inherited)_
Registers a callback function to be executed when an event is fired in a specific (emitter) object.
Events can be grouped in namespaces using `:`. When namespaced event is fired, it additionally fires all callbacks for that namespace.
```typescript
// myEmitter.on( ... ) is a shorthand for myEmitter.listenTo( myEmitter, ... ).
myEmitter.on( 'myGroup', genericCallback );
myEmitter.on( 'myGroup:myEvent', specificCallback );
// genericCallback is fired.
myEmitter.fire( 'myGroup' );
// both genericCallback and specificCallback are fired.
myEmitter.fire( 'myGroup:myEvent' );
// genericCallback is fired even though there are no callbacks for "foo".
myEmitter.fire( 'myGroup:foo' );
```
An event callback can [stop the event](module_utils_eventinfo-EventInfo.md#member-stop) and set the [return value](module_utils_eventinfo-EventInfo.md#member-return) of the [`fire`](#function-fire) method.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L475)
#### Type parameters
* `TEvent: extends BaseEvent`
The type describing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).
#### Parameters
* `emitter: Emitter`
The object that fires the event.
* `event: TEvent[ 'name' ]`
The name of the event.
* `callback: GetCallback`
The function to be called on event.
* `options?: GetCallbackOptions`
Additional options.
#### Returns
* `void`
### `off( event, callback ) → void` _(inherited)_
Stops executing the callback on the given event. Shorthand for [`this.stopListening( this, event, callback )`](#function-stopListening:BASE_STOP).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L444)
#### Parameters
* `event: string`
The name of the event.
* `callback: Function`
The function to stop being called.
#### Returns
* `void`
### `on( event, callback, options? ) → void` _(inherited)_
Registers a callback function to be executed when an event is fired.
Shorthand for [`this.listenTo( this, event, callback, options )`](#function-listenTo:BASE_EMITTER) (it makes the emitter listen on itself).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L416)
#### Type parameters
* `TEvent: extends BaseEvent`
The type descibing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).
#### Parameters
* `event: TEvent[ 'name' ]`
The name of the event.
* `callback: GetCallback`
The function to be called on event.
* `options?: GetCallbackOptions`
Additional options.
#### Returns
* `void`
### `once( event, callback, options? ) → void` _(inherited)_
Registers a callback function to be executed on the next time the event is fired only. This is similar to calling [`on`](#function-on) followed by [`off`](#function-off) in the callback.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L431)
#### Type parameters
* `TEvent: extends BaseEvent`
The type descibing the event. See [`BaseEvent`](module_utils_emittermixin-BaseEvent.md).
#### Parameters
* `event: TEvent[ 'name' ]`
The name of the event.
* `callback: GetCallback`
The function to be called on event.
* `options?: GetCallbackOptions`
Additional options.
#### Returns
* `void`
### `registerAttribute( attribute ) → void`
Registers a given attribute for the two-step caret movement.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L289)
#### Parameters
* `attribute: string`
Name of the attribute to handle.
#### Returns
* `void`
### `set( values ) → void` _(inherited)_
Creates and sets the value of an observable properties of this object. Such a property becomes a part of the state and is observable.
It accepts a single object literal containing key/value pairs with properties to be set.
This method throws the `observable-set-cannot-override` error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that `foo.set( 'bar', 1 )` may be slightly slower than `foo.bar = 1`.
In TypeScript, those properties should be declared in class using `declare` keyword. In example:
```typescript
public declare myProp1: number;
public declare myProp2: string;
constructor() {
this.set( {
'myProp1: 2,
'myProp2: 'foo'
} );
}
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L843)
#### Parameters
* `values: object & object`
An object with `name=>value` pairs.
#### Returns
* `void`
### `set( name, value ) → void` _(inherited)_
Creates and sets the value of an observable property of this object. Such a property becomes a part of the state and is observable.
This method throws the `observable-set-cannot-override` error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that `foo.set( 'bar', 1 )` may be slightly slower than `foo.bar = 1`.
In TypeScript, those properties should be declared in class using `declare` keyword. In example:
```typescript
public declare myProp: number;
constructor() {
this.set( 'myProp', 2 );
}
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L815)
#### Type parameters
* `K`
#### Parameters
* `name: K`
The property's name.
* `value: TwoStepCaretMovement[ K ]`
The property's value.
#### Returns
* `void`
### `stopDelegating( event?, emitter? ) → void` _(inherited)_
Stops delegating events. It can be used at different levels:
* To stop delegating all events.
* To stop delegating a specific event to all emitters.
* To stop delegating a specific event to a specific emitter.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L552)
#### Parameters
* `event?: string`
The name of the event to stop delegating. If omitted, stops it all delegations.
* `emitter?: Emitter`
(requires `event`) The object to stop delegating a particular event to. If omitted, stops delegation of `event` to all emitters.
#### Returns
* `void`
### `stopListening( emitter?, event?, callback? ) → void` _(inherited)_
Stops listening for events. It can be used at different levels:
* To stop listening to a specific callback.
* To stop listening to a specific event.
* To stop listening to all events fired by a specific object.
* To stop listening to all events fired by all objects.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/emittermixin.ts#L497)
#### Parameters
* `emitter?: Emitter`
The object to stop listening to. If omitted, stops it for all objects.
* `event?: string`
(Requires the `emitter`) The name of the event to stop listening to. If omitted, stops it for all events from `emitter`.
* `callback?: Function`
(Requires the `event`) The function to be removed from the call list for the given `event`.
#### Returns
* `void`
### `unbind( unbindProperties ) → void` _(inherited)_
Removes the binding created with [`bind`](#function-bind:SINGLE_BIND).
```typescript
// Removes the binding for the 'a' property.
A.unbind( 'a' );
// Removes bindings for all properties.
A.unbind();
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1090)
#### Parameters
* `unbindProperties: Array<'off' | 'set' | 'bind' | 'unbind' | 'decorate' | 'stopListening' | 'on' | 'once' | 'listenTo' | 'fire' | 'delegate' | 'stopDelegating' | 'destroy' | 'init' | 'editor' | 'isEnabled' | 'forceDisabled' | 'clearForceDisabled' | 'registerAttribute' | '_handleForwardMovement' | '_handleBackwardMovement'>`
Observable properties to be unbound. All the bindings will be released if no properties are provided.
#### Returns
* `void`
### `_handleBackwardMovement( eventData? ) → boolean` _(internal)_
Updates the document selection and the view according to the two–step caret movement state when moving **backwards**. Executed upon `keypress` in the [`EditingView`](module_engine_view_view-EditingView.md).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L371)
#### Parameters
* `eventData?: ViewDocumentDomEventData`
Data of the key press.
#### Returns
* `boolean`
`true` when the handler prevented caret movement
### `_handleForwardMovement( eventData? ) → boolean` _(internal)_
Updates the document selection and the view according to the two–step caret movement state when moving **forwards**. Executed upon `keypress` in the [`EditingView`](module_engine_view_view-EditingView.md).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L301)
#### Parameters
* `eventData?: ViewDocumentDomEventData`
Data of the key press.
#### Returns
* `boolean`
`true` when the handler prevented caret movement.
### `_enableClickingAfterNode() → void` _(private)_
Starts listening to [event-mousedown](module_engine_view_document-ViewDocument.md#event-mousedown) and [event-selectionChange](module_engine_view_document-ViewDocument.md#event-selectionChange) and puts the selection before/after a 2-step node if clicked at the beginning/ending of the 2-step node.
The purpose of this action is to allow typing around the 2-step node directly after a click.
See https\://github.com/ckeditor/ckeditor5/issues/1016.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L495)
#### Returns
* `void`
### `_enableInsertContentSelectionAttributesFixer() → void` _(private)_
Starts listening to [event-insertContent](module_engine_model_model-Model.md#event-insertContent) and corrects the model selection attributes if the selection is at the end of a two-step node after inserting the content.
The purpose of this action is to improve the overall UX because the user is no longer "trapped" by the two-step attribute of the selection, and they can type a "clean" (`linkHref`–less) text right away.
See https\://github.com/ckeditor/ckeditor5/issues/6053.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L575)
#### Returns
* `void`
### `_handleDeleteContentAfterNode() → void` _(private)_
Starts listening to [`deleteContent`](module_engine_model_model-Model.md#function-deleteContent) and checks whether removing a content right after the tow-step attribute.
If so, the selection should not preserve the two-step attribute. However, if the [`TwoStepCaretMovement`](module_typing_twostepcaretmovement-TwoStepCaretMovement.md) plugin is active and the selection has the two-step attribute due to overridden gravity (at the end), the two-step attribute should stay untouched.
The purpose of this action is to allow removing the link text and keep the selection outside the link.
See https\://github.com/ckeditor/ckeditor5/issues/7521.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L605)
#### Returns
* `void`
### `_overrideGravity() → void` _(private)_
Overrides the gravity using the [model writer](module_engine_model_writer-ModelWriter.md) and stores the information about this fact in the [`_overrideUid`](#member-_overrideUid).
A shorthand for [`overrideSelectionGravity`](module_engine_model_writer-ModelWriter.md#function-overrideSelectionGravity).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L677)
#### Returns
* `void`
### `_restoreGravity() → void` _(private)_
Restores the gravity using the [model writer](module_engine_model_writer-ModelWriter.md).
A shorthand for [`restoreSelectionGravity`](module_engine_model_writer-ModelWriter.md#function-restoreSelectionGravity).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-typing/src/twostepcaretmovement.ts#L688)
#### Returns
* `void`
## Events
### `change:isEnabled( eventInfo, name, value, oldValue )` _(inherited)_
Fired when the `isEnabled` property changed value.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L51)
#### Parameters
* `eventInfo: EventInfo`
An object containing information about the fired event.
* `name: string`
Name of the changed property (`isEnabled`).
* `value: boolean`
New value of the `isEnabled` property with given key or `null`, if operation should remove property.
* `oldValue: boolean`
Old value of the `isEnabled` property with given key or `null`, if property was not set before.
### `change:{property}( eventInfo, name, value, oldValue )` _(inherited)_
Fired when a property changed value.
```typescript
observable.set( 'prop', 1 );
observable.on>( 'change:prop', ( evt, propertyName, newValue, oldValue ) => {
console.log( `${ propertyName } has changed from ${ oldValue } to ${ newValue }` );
} );
observable.prop = 2; // -> 'prop has changed from 1 to 2'
```
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1190)
#### Parameters
* `eventInfo: EventInfo`
An object containing information about the fired event.
* `name: string`
The property name.
* `value: TValue`
The new property value.
* `oldValue: TValue`
The previous property value.
### `set:isEnabled( eventInfo, name, value, oldValue )` _(inherited)_
Fired when the `isEnabled` property is going to be set but is not set yet (before the `change` event is fired).
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-core/src/plugin.ts#L51)
#### Parameters
* `eventInfo: EventInfo`
An object containing information about the fired event.
* `name: string`
Name of the changed property (`isEnabled`).
* `value: boolean`
New value of the `isEnabled` property with given key or `null`, if operation should remove property.
* `oldValue: boolean`
Old value of the `isEnabled` property with given key or `null`, if property was not set before.
### `set:{property}( eventInfo, name, value, oldValue )` _(inherited)_
Fired when a property value is going to be set but is not set yet (before the `change` event is fired).
You can control the final value of the property by using the [event's `return` property](module_utils_eventinfo-EventInfo.md#member-return).
```typescript
observable.set( 'prop', 1 );
observable.on>( 'set:prop', ( evt, propertyName, newValue, oldValue ) => {
console.log( `Value is going to be changed from ${ oldValue } to ${ newValue }` );
console.log( `Current property value is ${ observable[ propertyName ] }` );
// Let's override the value.
evt.return = 3;
} );
observable.on>( 'change:prop', ( evt, propertyName, newValue, oldValue ) => {
console.log( `Value has changed from ${ oldValue } to ${ newValue }` );
} );
observable.prop = 2; // -> 'Value is going to be changed from 1 to 2'
// -> 'Current property value is 1'
// -> 'Value has changed from 1 to 3'
```
**Note:** The event is fired even when the new value is the same as the old value.
[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-utils/src/observablemixin.ts#L1228)
#### Parameters
* `eventInfo: EventInfo`
An object containing information about the fired event.
* `name: string`
The property name.
* `value: TValue`
The new property value.
* `oldValue: TValue`
The previous property value.
---
Full index of the CKEditor 5 API reference: [llms.txt](llms.txt)