What does the wording “in capillis” mean?

What does the wording “in capillis” mean?

While analyzing documents from the 18th century, or before, we may read sometimes the wording “in capillis” referred to a woman, often listed as daughter or sister of a head of the family. So we may read respectively “figlia in capillis” or “sorella in capillis”. This literally means “in her hair” that, out of its…