[NTG-context] Captions with background

```Hi,

in my books I typeset captions onto full page images, therefore I need a
background; in the attached example it’s just a white box, usually I use a
MetaPost shadow (some of you helped me with that a few years ago, current code
```
Now, the background should just enclose the text, not more. Since I don’t know
how long the caption will be (I use the whole setup in a macro), I need a \vbox
within \setlayer, but that always uses the full \textwidth, regardless of width
settings of \framed.

If the caption is short, the box should be minimal. Is this possible?

Even better would be a textbackground just behind the text lines.

Unfortunately my MP foo is not up to the task, the rectangular shadow was hard
enough, but I’d try.
There’s an example in details.pdf, but I don’t understand how I could
manipulate the path around the text (not: paragraph).

The example shows another problem: If you run it with --mode=arrange, the bleed
is cut off.
Is this a matter of settings or a bug?

Greetlings, Hraban
```

captiontest.tex
Description: Binary data

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