Gets the export value of each widget in Kids order (Opt, inheritable, PDF 1.4); empty when absent.
public IReadOnlyList<string> Options { get; }
ISO 32000-2 §12.7.5.2.3, Table 230. An element that is not a text string reads as an empty string, and an array whose length
differs from the number of widgets records ButtonOptLengthMismatch; both keep positions aligned with Kids.