I might need a little more help just to understand how best to adapt 
this to my situation:

One thing is clear: I was attempting to use a 'list' variable, and I can 
see why that was an error, since it is headertexts, not TOC that I want 
to influence.

But let me simplify my situation:

You seem to suggest initially that I could use \structureuservariable 
(or \structurevariable) instead, especially since I already have a 
variable to call on, e.g \startchapter[title={My title}][author={A. 
uthor}]. But in the example you then gave, you made no use of either of 
these.

My current setting is:

\setupheadertexts   [{\hfill\getmarking[chapter]\hfill}][]   
[{\hfill\documentvariable{metadata:title}\hfill}][]

which gives me the book title centred on verso pages, and the chapter 
title centred on recto pages. All I want to do is to have the chapter 
contributors' name for each chapter instead of the chapter title.

So why can't I create a setups along the lines of:

\startsetups[contributor] \getmarking[\structureuservariable{author}] 
\stopsetups

Then just swap 'chapter' in \setupheadertexts, with 'contributor'? I 
tried it but it doesn't work. I thought it would be logical. Clearly I'm 
wrong but don't appreciate why.

Julian

On 18/3/22 18:52, Henning Hraban Ramm via ntg-context wrote:
> The *list* variables work only in lists.
>
> There’s also \structurevariable and \structureuservariable.
>
> Make sure you use setups for the header, otherwise the variable gets 
> expanded only once at the beginning.
>
> Like in:
>
> \setuppagenumbering[alternative=doublesided]
> \setupheadertexts[] % empty
> \setupheadertexts[\setups{text right}][][][\setups{text left}]
>
> \startsetups[text right]
> \rlap{\pagenumber}
> \hfill
> \getmarking[chapter]
> \hfill
> \llap{Un Nom}
> \stopsetups
>
> \startsetups[text left]
> \rlap{Una Person}
> \hfill
> \getmarking[section]
> \hfill
> \llap{\pagenumber}
> \stopsetups