Of course it works, it's the order.
For me TeX wouldn't be the same without you. Thank you very much Hans.

Hans Hagen via ntg-context <ntg-context@ntg.nl> schrieb am Mo., 25. Juli
2022, 09:20:

> On 7/24/2022 11:35 PM, cryo shock via ntg-context wrote:
> > Hey there,
> >
> > I am having trouble understanding some basic blank page behavior. I hope
> > that somebody of you can point me in the right direction.
> >
> > My primary goal is to create application documents consisting of various
> > .tex components and with external PDF pages inserted as well. The second
> > part of that goal is to use multiple-level bookmarking as well.
> > Bookmarking should look like this:
> >
> > - Letter
> > - Resume
> > - Testimonies
> > -- Testimony A
> > -- Testimony B
> > -- Testimony C
> >
> > In the following MWE you can see my progress along with some notes to
> > help understanding.
> >
> > There are two questions, I'd wish could be answered:
> >
> > 1. Why does TeX insert a blank page before a pagefigure I enclose within
> > a (hidden) head?
> >
> > 2. Can the \bookmark[list]{text} command be somehow used for multi-level
> > bookmarking?
> >
> > While the first question would make up for a more consistent solution,
> > the second question would do the job as well.
> >
> > I hope some of you can enlighten me.
> >
> > Cheers, k
> >
> >
> > %%% START of MWE
> >
> > \definehead[VisiSection][section]
> > \setuphead[VisiSection][number=no]
> >
> > \definehead[InvisiSection][VisiSection]
> > \setuphead[InvisiSection][placehead=no]
> >
> > \definelist[CustomBMarks]
> >
> > \setupinteraction[state=start]
> > \placebookmarks[VisiSection,InvisiSection,CustomBMarks]
> >
> > \startcomponent * % not a product, no
> >    \startVisiSection[title={Custom Section A}]
> >      Text of Custom Section A
> >    \stopVisiSection
> >    \page
> >    \startVisiSection[title={Custom Section B}]
> >      Text of Custom Section B
> >    \stopVisiSection
> >    \startInvisiSection[title={Hidden Custom Section A}]
> >      Text of Hidden Custom Section A
> >    \stopInvisiSection
> >    \page
> >    \startInvisiSection[title={Hidden Custom Section B}]
> >      Text of Hidden Custom Section B
> >    \stopInvisiSection
> >    \page
> >    TEST\bookmark[CustomBMarks]{Start of Teststack} \dorecurse{800}{TEST
> > }NEEDLE\bookmark[CustomBMarks]{Needle in the Teststack}
> > \dorecurse{400}{TEST }TEST.\bookmark[CustomBMarks]{End of Teststack}
> >    %%%
> >    %%% So far no problems.
> >    %%% The following combination does the job, but I see no possibility
> >    %%% to arrange the "CustomBMarks"-list in multi-levels.
> >    %%%
> >    \page
> >    \startstandardmakeup
> >      \filterpages[{test.pdf}][1]\bookmark[CustomBMarks]{Pagefigure}
> >    \stopstandardmakeup
> >    %%%
> >    %%% So the following method would be the best choice to work with
> >    %%% multi-level bookmarks. But as soon as I start working with
> >    %%% (custom) heads together with pagefigures, CTX places a blank
> >    %%% page before every figure...
> >    %%% Note: you don't need a dummy file. The last (unnumbered) page is
> >    %%% the wanted external PDF. The numbered page before is the unwanted
> > one.
> >    %%%
> >    \startInvisiSection[title={External Testpage A}]
> >      \startstandardmakeup
> >        \filterpages[{test.pdf}][1]
> >      \stopstandardmakeup
> >    \stopInvisiSection
> > \stopcomponent
> because even a hidden head is something (anchor on page), you can try this:
>
>      \startstandardmakeup
>    \startInvisiSection[title={External Testpage A}]
>        \filterpages[{test.pdf}][1]
>    \stopInvisiSection
>      \stopstandardmakeup
>
> -----------------------------------------------------------------
>                                            Hans Hagen | PRAGMA ADE
>                Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>         tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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