Dear Friends,
I spent some time searching and coding simple documents, but failed and
therefore I'm asking for help...
A section such as chapter cn have custom keys with values. One uses the:
\structureuservariable command to access such values.
How can I use such a value to create a custom header in a format:
Prefix: \structureuservariable{foo}

I am asking for the only thing that worked when I tried was calling the:
\setupheadertexts command inside a chapter environment block with some
prefix. Unfortunately the value from the custom field was not expanded.
It was correctly inserted in a regular paragraph.
For example:
\startchapter
[title={A sample title}][custom_something={random_value}]
...
\stopchapter

How can I put the value of: custom_something in the header with some prefix?

All the best and thanks,
Pawel