src/vs/editor/common/core/textChange.ts/TextChangeCompressor/_splitPrev
class TextChangeCompressor:	private static _splitPrev(edit: TextChange, offset: number): [TextChange, TextChange] {
		const preText = edit.newText.substr(0, offset);
		const postText = edit.newText.substr(offset);

		return [
			new TextChange(
				edit.oldPosition,
				edit.oldText,
				edit.newPosition,
				preText
			),
			new TextChange(
				edit.oldEnd,
				'',
				edit.newPosition + offset,
				postText
			)
		];
	}