Gets or sets the style flags (F, PDF 1.4); as stored when read, 0 when absent or not an integer.
public PdfOutlineItemFlags Flags { get; set; }
ISO 32000-2 §12.3.3, Tables 151 and 152: "all other bits of the integer shall be 0". Setting
None removes F, the default; any other value raises a later save of a document below
PDF 1.4 to 1.4.