Because this seems to be a topic that has several people hitting the panic button, here is how to pee while wearing your wedding dress. Because this exceeds the maximum character limit, it will be in two parts.
On arrival at your venue
* Open the door of the ladies' room and look in. If the floor is not clean, call the venue staff and ask to have it cleaned.
* If the floor is clean, walk into the ladies' room and open the door of the handicapped stall. If the floor of the handicapped stall is not clean, call the venue staff and ask to have it cleaned.
This ensures that you will not later get the train/back of the dress dirty just by having it touch the floor.