PDF-Hul doesn't check /Tabs key value in /Page dictionary.

[asciim0]

JHOVE does not check the correct usage of the /Tabs key in the page object.
As per ISO 32000 the Tabs key is optional. If present, the possible values shall be (as per 32000-2):
R, C, S, A or W (see 7.7.3.3 Table 31 and 12.5.1 in ISO 32000-2:2017).
The Tabs key determines the tab navigation order of annotations on a page.

Further information is also contained in the according pdfcpu issue: pdfcpu/pdfcpu#618

The expectation is that:

• if no Tab key is present --> no implication on validation status
• if Tab key is present but not correctly filled --> well-formed, but not valid