How Is the “First Time” Filter Calculated for fn_purchase Events with Additional Property Filters?

when applying the “First Time” filter to the fn_purchase event with an additional property filter (e.g. plan_type = X), how is it calculated? Does it count: 1. Users whose very first purchase in their lifetime matches the filter, or 2. Users’ first occurrence of fn_purchase that matches the applied filter, even if they have previous purchases that do not match the filter?