src/vs/editor/browser/controller/textAreaInput.ts/CompositionContext/handleCompositionUpdate
class CompositionContext:	public handleCompositionUpdate(text: string | null | undefined): ITypeData {
		text = text || '';
		const typeInput: ITypeData = {
			text: text,
			replacePrevCharCnt: this._lastTypeTextLength,
			replaceNextCharCnt: 0,
			positionDelta: 0
		};
		this._lastTypeTextLength = text.length;
		return typeInput;
	}