Dunbundle command processes repeating groups. See the manual Dunbundle for the detail.

The command argument leaf-field-list:

word

provides field names to be "unbundled". In this case, it means:

• for each occurence of "word" field, create a new record with it and other fields (in this case "chapter" field).

About the leaf-field-list, see the manual Dintro and also D_lsa for the detail.