What does the value `/W` mean in PDF `/Tabs` key?

Question

According to the PDF 1.7 specifications, a PDF may only have the values /R, /C and /S on the /Tabs key of a page object (see PDF reference Page 145, Table 3.27).

I have a PDF in front of me that fails in PDF structure preflight with a value /W for Tabs.

I could not find the value in the specs I have, so I ask here if someone can shed some light on this?

Thanks!

Answer 1

The W and A names are going to be introduced in PDF 2.0:

[...]Beginning with PDF 2.0, the possible values also include A (annotations array order) and W (widget order). Annotations array order refers to the order of the annotation enumerated in the Annots entry of the Page dictionary [...]. Widget order means using the same array ordering but making two passes, the first only picking the widget annotations and the second picking all other annotations.

(quoted from a draft of PDF 2.0)