COinS stands for "ContextObjects in Spans", and is a method for embedding bibliographic information in HTML. The Pickers can read COinS directly and inserts a footer that lets you export information automatically.
If you look at the source code of a Web page and search for "Z3988", you can see the information that is available for the Picker to export. Unfortunately, not all Web-based databases provide complete COinS information, which is why the data may be incomplete when it is imported into Citavi. Especially problematic are reference types that COinS does differentiate as fully as Citavi does.
When you import by using the footer, please make sure to carefully double check the bibliographic information.