[NTG-context] context.delayed as parameter of setuphead[before=...]

Dear List, I'm trying to mirror the context command `\setuphead[chapter][before=hello]` into lua with delayed typesetting of 'hello', but `\ctxlua{context.setuphead({'chapter'}, {before=context.delayed'hello'})}` does not have any effect. Could anyone help me on this? Thanks! Best, Sylvain