You can see the valid values for any property in the current data set. For example, suppose a parcel has the property IS_OWNER_OCCUPIED. If you are unfamiliar with the data, you would not know the valid values for this property. They could be Yes and No, True and False, Y and N, or T and F. You can view and insert the possible values for this property from the Properties pane.
Some properties have many values, which can take a long time to retrieve. In some cases, a warning is displayed. You can retrieve the values anyway, or cancel the retrieval.
You cannot view or insert values when you are creating a calculation or an expression for a label.