src/vs/editor/contrib/gotoSymbol/referencesModel.ts/FilePreview/preview
class FilePreview:	preview(range: IRange, n: number = 8): { value: string; highlight: IMatch } | undefined {
		const model = this._modelReference.object.textEditorModel;

		if (!model) {
			return undefined;
		}

		const { startLineNumber, startColumn, endLineNumber, endColumn } = range;
		const word = model.getWordUntilPosition({ lineNumber: startLineNumber, column: startColumn - n });
		const beforeRange = new Range(startLineNumber, word.startColumn, startLineNumber, startColumn);
		const afterRange = new Range(endLineNumber, endColumn, endLineNumber, Constants.MAX_SAFE_SMALL_INTEGER);

		const before = model.getValueInRange(beforeRange).replace(/^\s+/, '');
		const inside = model.getValueInRange(range);
		const after = model.getValueInRange(afterRange).replace(/\s+$/, '');

		return {
			value: before + inside + after,
			highlight: { start: before.length, end: before.length + inside.length }
		};
	}