\setupinteraction[state=start]
\setupregister[index][n=1]

\starttext
My \index{dog}dog is a \index{dog+bullterrier}bullterrier.
He doesn't like \index{cat}cats.
There are a lot of \index{cat+stray}stray cats, but only a few of them are \index{cat+Siamese}Siamese. I don’t think there are \index{cat+Burmese}Burmese cats.

\seeindex{cat+obese}{cat+Siamese}
\seeindex{hound}{dog}

\completeindex

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