Create the entity with a composition, e.g. Order and list of OrderLine in it.
Create a XLSX report using the wizard. Add a tabular region for order lines.
AR: When the report editor is opened the List of entities parameter name combo box is empty, but in fact the parameter name seems to be entity#lines (this may be discovered in the XML field of the report entity)
ER: List of entities parameter name combo box contains entity#lines
Platform version: 7.2.11
sample project: cuba-reports-sample.zip