Oh,
I think I may have spoken, or written too fast. It is when you create a Layout. Here you have the Layout Setup window
In Show records from you select a TO (Table Occurrence) which represents a Table.
Reason is you need to select a field on the Layout to work with properties on the Data tab. For example, if no field is selected on the Layout, most of the fields on the Field section of the Data Tab are greyed out
for example Show data from and Control Style. Now if I select the Référence field on my Layout
the fields are not greyed out.