engine/model/utils/modifyselection

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 instead of this function. This function is only exposed to be reusable in algorithms which change the modifySelection method's behavior.

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