[NTG-context] Trouble with Index

So far I have not succeded to make an index in a book I am typesetting. I write something like: \starttext \defineregister[index][indices] \index[Tantrum]Tantrums can be normal for \index[tantrum][tantrum+toddlers]toddlers. Young children have them for many reasons like being tired, feeling out of control, over-stimulated, or wanting something they can't have. General hints: Toddlers and preschoolers cannot regulate themselves because they don't yet know their own limits. \completeindex \stoptext And the message I get is: "index not found/processed". In the pdf appears a page with Index but no entries.