This parameter is set to true, if the field has one and only one selection (not 0 and not more than 1).
If this property is set to true, the field cannot be cleared anymore and no more selections can be performed in that field.
The property _OneAndOnlyOne_ can be set to true if one and only value has been selected in the field prior to setting the property.
This parameter is set to true, if the field has one and only one selection (not 0 and not more than 1). If this property is set to true, the field cannot be cleared anymore and no more selections can be performed in that field.