# engine/model/utils/modifyselection

module

<a id="functions">

## Functions

<a id="function-modifySelection">

### `modifySelection( model, selection, options = { options.direction?, options.treatEmojiAsSingleUnit?, options.unit? } ) → void` _(internal)_

Modifies the selection. Currently, the supported modifications are:

* Extending. The selection focus is moved in the specified `options.direction` with a step specified in `options.unit`. Possible values for `unit` are:
* `'character'` (default) - moves selection by one user-perceived character. In most cases this means moving by one character in `String` sense. However, unicode also defines "combing marks". These are special symbols, that combines with a symbol before it ("base character") to create one user-perceived character. For example, `q̣̇` is a normal letter `q` with two "combining marks": upper dot (`Ux0307`) and lower dot (`Ux0323`). For most actions, i.e. extending selection by one position, it is correct to include both "base character" and all of it's "combining marks". That is why `'character'` value is most natural and common method of modifying selection.
* `'codePoint'` - moves selection by one unicode code point. In contrary to, `'character'` unit, this will insert selection between "base character" and "combining mark", because "combining marks" have their own unicode code points. However, for technical reasons, unicode code points with values above `UxFFFF` are represented in native `String` by two characters, called "surrogate pairs". Halves of "surrogate pairs" have a meaning only when placed next to each other. For example `𨭎` is represented in `String` by `\uD862\uDF4E`. Both `\uD862` and `\uDF4E` do not have any meaning outside the pair (are rendered as ? when alone). Position between them would be incorrect. In this case, selection extension will include whole "surrogate pair".
* `'word'` - moves selection by a whole word.

**Note:** if you extend a forward selection in a backward direction you will in fact shrink it.

**Note:** Use [`modifySelection`](module_engine_model_model-Model.md#function-modifySelection) instead of this function. This function is only exposed to be reusable in algorithms which change the [`modifySelection`](module_engine_model_model-Model.md#function-modifySelection) method's behavior.

[See source](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-engine/src/model/utils/modifyselection.ts#L59)

#### Parameters

* `model: Model`

  The model in context of which the selection modification should be performed.

* `selection: ModelSelection | ModelDocumentSelection`

  The selection to modify.

* `options: object`

  Properties

  * `options.direction?: 'forward' | 'backward'`

    The direction in which the selection should be modified. Default 'forward'.

  * `options.treatEmojiAsSingleUnit?: boolean`

    Whether multi-characer emoji sequences should be handled as single unit.

  * `options.unit?: 'character' | 'codePoint' | 'word'`

    The unit by which selection should be modified. Default 'character'.

  Defaults to `{}`

#### Returns

* `void`

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Full index of the CKEditor 5 API reference: [llms.txt](llms.txt)