Non-ambiguous expression

If a variable exists more than once in the lookups, then this option would insert a non-ambiguous expression for the text.  For example, Bicycle is in the Type of Collision field, and in the Type of Vehicle field.  If you wanted to create a filter for the Type of Collision field you would create this expression by using the non-ambiguous expression button:

Type_of_Collision = Type_of_Collision.Bicycle

This would ensure that the field you wanted would be used for the filter.